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"),s("p",[t._v("当映射的计算属性的名称与 state 的子节点名称相同时，我们也可以给 "),s("code",[t._v("mapState")]),t._v(" 传一个字符串数组。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("computed")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("mapState")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 映射 this.count 为 store.state.count")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'count'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("h4",{attrs:{id:"对象展开运算符"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#对象展开运算符"}},[t._v("#")]),t._v(" 对象展开运算符")]),t._v(" "),s("p",[s("code",[t._v("mapState")]),t._v(" 函数返回的是一个对象。可使用对象展开运算符将此对象混入到外部对象中")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("computed")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("localComputed")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("h3",{attrs:{id:"getter"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#getter"}},[t._v("#")]),t._v(" Getter")]),t._v(" "),s("p",[t._v("有时候我们需要从 store 中的 state 中派生出一些状态，例如对列表进行过滤并计数：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("computed")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("doneTodosCount")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("如果有多个组件需要用到此属性，我们要么复制这个函数，或者抽取到一个共享函数然后在多处导入它——无论哪种方式都不是很理想。")]),t._v(" "),s("p",[t._v("Vuex 允许我们在 store 中定义“getter”（"),s("strong",[t._v("可以认为是 store 的计算属性")]),t._v("）。就像计算属性一样，getter 的返回值会根据它的依赖"),s("strong",[t._v("被缓存")]),t._v("起来，且只有当它的依赖值发生了改变才会被重新计算。")]),t._v(" "),s("p",[t._v("Getter 接受 state 作为其第一个参数：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" store "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br")])]),s("h4",{attrs:{id:"通过属性访问"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#通过属性访问"}},[t._v("#")]),t._v(" 通过属性访问")]),t._v(" "),s("p",[t._v("Getter 会暴露为 "),s("code",[t._v("store.getters")]),t._v(" 对象，你可以以属性的形式访问这些值：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("store"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("getters"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("doneTodos "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// -> [{ id: 1, text: '...', done: true }]")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("Getter 也可以接受其他 getter 作为第二个参数：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("getters")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("doneTodosCount")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" getters")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=>")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" getters"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("doneTodos"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("length\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\nstore"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("getters"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("doneTodosCount "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// -> 1")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[t._v("我们可以很容易地在任何组件中使用它：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("computed")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("doneTodosCount")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("$store"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("getters"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("doneTodosCount\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("注意，getter 在通过属性访问时是作为 Vue 的响应式系统的一部分缓存其中的。")]),t._v(" "),s("h4",{attrs:{id:"通过方法访问"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#通过方法访问"}},[t._v("#")]),t._v(" 通过方法访问")]),t._v(" "),s("p",[t._v("你也可以通过让 getter 返回一个函数，来"),s("strong",[t._v("实现给 getter 传参")]),t._v("。在你对 store 里的数组进行查询时非常有用。")]),t._v(" "),s("div",{staticClass:"language-js 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[t._v("注意，getter 在通过方法访问时，每次都会去进行调用，而"),s("strong",[t._v("不会缓存结果")]),t._v("。")]),t._v(" "),s("h4",{attrs:{id:"mapgetters-辅助函数"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#mapgetters-辅助函数"}},[t._v("#")]),t._v(" "),s("code",[t._v("mapGetters")]),t._v(" 辅助函数")]),t._v(" "),s("p",[s("code",[t._v("mapGetters")]),t._v(" 辅助函数仅仅是将 store 中的 getter 映射到局部计算属性：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("h3",{attrs:{id:"mutation"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#mutation"}},[t._v("#")]),t._v(" Mutation")]),t._v(" "),s("p",[t._v("更改 Vuex 的 store 中的状态的"),s("strong",[t._v("唯一方法")]),t._v("是提交 mutation。Vuex 中的 mutation 非常类似于事件：每个 mutation 都有一个字符串的 "),s("strong",[t._v("事件类型 (type)")]),t._v(" 和 一个 "),s("strong",[t._v("回调函数 (handler)")]),t._v("。这个回调函数就是我们实际进行状态更改的地方，并且它会接受 state 作为第一个参数：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" store "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" 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"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("mutations")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("increment")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n      "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 变更状态")]),t._v("\n      state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("count"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token 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时，调用此函数。”要唤醒一个 mutation handler，你需要以相应的 type 调用 "),s("strong",[t._v("store.commit")]),t._v(" 方法：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("store"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("commit")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'increment'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("h4",{attrs:{id:"提交载荷-payload"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#提交载荷-payload"}},[t._v("#")]),t._v(" 提交载荷（Payload）")]),t._v(" "),s("p",[t._v("你可以向 "),s("code",[t._v("store.commit")]),t._v(" 传入额外的参数，即 mutation 的 "),s("strong",[t._v("载荷（payload）")]),t._v("：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("mutations")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("increment")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" n")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("count "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[t._v("在大多数情况下，载荷应该是一个对象，这样可以包含多个字段并且记录的 mutation 会更易读：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("mutations")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'increment'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("amount")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br")])]),s("h4",{attrs:{id:"对象风格的提交方式"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#对象风格的提交方式"}},[t._v("#")]),t._v(" 对象风格的提交方式")]),t._v(" "),s("p",[t._v("提交 mutation 的另一种方式是直接使用包含 "),s("code",[t._v("type")]),t._v(" 属性的对象：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("store"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[t._v("当使用对象风格的提交方式，整个对象都作为载荷传给 mutation 函数，因此 handler 保持不变：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("mutations")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("increment")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" payload")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("count "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+=")]),t._v(" payload"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("amount\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("h4",{attrs:{id:"mutation-需遵守-vue-的响应规则"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#mutation-需遵守-vue-的响应规则"}},[t._v("#")]),t._v(" Mutation 需遵守 Vue 的响应规则")]),t._v(" "),s("p",[t._v("既然 Vuex 的 store 中的状态是响应式的，那么当我们变更状态时，监视状态的 Vue 组件也会自动更新。这也意味着 Vuex 中的 mutation 也需要与使用 Vue 一样遵守一些注意事项：")]),t._v(" "),s("ol",[s("li",[t._v("最好提前在你的 store 中初始化好所有所需属性。")]),t._v(" "),s("li",[t._v("当需要在对象上添加新属性时，你应该")])]),t._v(" "),s("ul",[s("li",[s("p",[t._v("使用 "),s("code",[t._v("Vue.set(obj, 'newProp', 123)")]),t._v(", 或者")])]),t._v(" "),s("li",[s("p",[t._v("以新对象替换老对象。例如，利用"),s("a",{attrs:{href:"https://github.com/tc39/proposal-object-rest-spread",target:"_blank",rel:"noopener noreferrer"}},[t._v("对象展开运算符"),s("OutboundLink")],1),t._v("我们可以这样写：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("obj "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("...")]),t._v("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("obj"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("newProp")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("123")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])])])]),t._v(" "),s("h4",{attrs:{id:"使用常量替代-mutation-事件类型"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#使用常量替代-mutation-事件类型"}},[t._v("#")]),t._v(" 使用常量替代 Mutation 事件类型")]),t._v(" "),s("p",[t._v("使用常量替代 mutation 事件类型在各种 Flux 实现中是很常见的模式。这样可以使 linter 之类的工具发挥作用，同时把这些常量放在单独的文件中可以让你的代码合作者对整个 app 包含的 mutation 一目了然：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// mutation-types.js")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("export")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("SOME_MUTATION")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'SOME_MUTATION'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// store.js")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("import")]),t._v(" Vuex "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("from")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'vuex'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("import")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("SOME_MUTATION")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("from")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'./mutation-types'")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token 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property"}},[t._v("mutations")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 我们可以使用 ES2015 风格的计算属性命名功能来使用一个常量作为函数名")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("SOME_MUTATION")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n      "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// mutate state")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br"),s("span",{staticClass:"line-number"},[t._v("14")]),s("br"),s("span",{staticClass:"line-number"},[t._v("15")]),s("br")])]),s("p",[t._v("用不用常量取决于你——在需要多人协作的大型项目中，这会很有帮助。但如果你不喜欢，你完全可以不这样做。")]),t._v(" "),s("h4",{attrs:{id:"mutation-必须是同步函数"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#mutation-必须是同步函数"}},[t._v("#")]),t._v(" Mutation 必须是同步函数")]),t._v(" "),s("p",[t._v("一条重要的原则就是要记住 "),s("strong",[t._v("mutation 必须是同步函数")]),t._v("。为什么？请参考下面的例子：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("mutations")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("someMutation")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    api"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("callAsyncMethod")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=>")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n      state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("count"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[t._v("现在想象，我们正在 debug 一个 app 并且观察 devtool 中的 mutation 日志。每一条 mutation 被记录，devtools 都需要捕捉到前一状态和后一状态的快照。然而，在上面的例子中 mutation 中的异步函数中的回调让这不可能完成：因为当 mutation 触发的时候，回调函数还没有被调用，devtools 不知道什么时候回调函数实际上被调用——实质上任何在回调函数中进行的状态的改变都是不可追踪的。")]),t._v(" "),s("h4",{attrs:{id:"在组件中提交-mutation-mapmutations辅助函数"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#在组件中提交-mutation-mapmutations辅助函数"}},[t._v("#")]),t._v(" 在组件中提交 Mutation  ("),s("code",[t._v("mapMutations")]),t._v("辅助函数)")]),t._v(" "),s("p",[t._v("你可以在组件中使用 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"),s("a",{attrs:{href:"https://vuex.vuejs.org/zh/guide/actions.html",target:"_blank",rel:"noopener noreferrer"}},[t._v("Action"),s("OutboundLink")],1),t._v("。")]),t._v(" "),s("h3",{attrs:{id:"action"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#action"}},[t._v("#")]),t._v(" Action")]),t._v(" "),s("p",[t._v("Action 类似于 mutation，不同在于：")]),t._v(" "),s("ul",[s("li",[t._v("Action 提交的是 mutation，而不是直接变更状态。")]),t._v(" "),s("li",[t._v("Action 可以包含任意异步操作。")])]),t._v(" "),s("p",[t._v("让我们来注册一个简单的 action：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" store "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Vuex"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("h4",{attrs:{id:"分发-action"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#分发-action"}},[t._v("#")]),t._v(" 分发 Action")]),t._v(" "),s("p",[s("strong",[t._v("Action 通过 "),s("code",[t._v("store.dispatch")]),t._v(" 方法触发")]),t._v("：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("store"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("dispatch")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token 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function"}},[t._v("setTimeout")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=>")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("commit")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'someMutation'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("resolve")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n      "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br")])]),s("p",[t._v("现在你可以：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("store"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("dispatch")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("在另外一个 action 中也可以：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("actions")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("actionB")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br")])]),s("p",[t._v("最后，如果我们利用 "),s("a",{attrs:{href:"https://tc39.github.io/ecmascript-asyncawait/",target:"_blank",rel:"noopener noreferrer"}},[t._v("async / await"),s("OutboundLink")],1),t._v("，我们可以如下组合 action：")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 假设 getData() 和 getOtherData() 返回的是 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br")])]),s("blockquote",[s("p",[t._v("一个 "),s("code",[t._v("store.dispatch")]),t._v(" 在不同模块中可以触发多个 action 函数。在这种情况下，只有当所有触发函数完成后，返回的 Promise 才会执行。")])]),t._v(" "),s("h2",{attrs:{id:"更多"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#更多"}},[t._v("#")]),t._v(" 更多")]),t._v(" "),s("p",[t._v("更多内容查看官方文档："),s("a",{attrs:{href:"https://vuex.vuejs.org/zh/guide/modules.html",target:"_blank",rel:"noopener noreferrer"}},[t._v("https://vuex.vuejs.org/zh/guide/modules.html"),s("OutboundLink")],1)])])}),[],!1,null,null,null);s.default=e.exports}}]);