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function"}},[t._v("fetchPosts")]),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(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("then")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("response")]),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("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setState")]),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 literal-property property"}},[t._v("posts")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" response"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("posts\n      "),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("\n    "),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("\n\n    "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("fetchComments")]),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(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("then")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("response")]),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("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setState")]),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 literal-property property"}},[t._v("comments")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" response"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("comments\n      "),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("\n    "),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("\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("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("span",{staticClass:"line-number"},[t._v("16")]),s("br"),s("span",{staticClass:"line-number"},[t._v("17")]),s("br"),s("span",{staticClass:"line-number"},[t._v("18")]),s("br"),s("span",{staticClass:"line-number"},[t._v("19")]),s("br"),s("span",{staticClass:"line-number"},[t._v("20")]),s("br"),s("span",{staticClass:"line-number"},[t._v("21")]),s("br"),s("span",{staticClass:"line-number"},[t._v("22")]),s("br")])]),s("p",[t._v("这里的合并是浅合并，所以 "),s("code",[t._v("this.setState({comments})")]),t._v(" 完整保留了 "),s("code",[t._v("this.state.posts")]),t._v("， 但是完全替换了 "),s("code",[t._v("this.state.comments")]),t._v("。")]),t._v(" "),s("h2",{attrs:{id:"数据是向下流动的-单向数据流"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#数据是向下流动的-单向数据流"}},[t._v("#")]),t._v(" 数据是向下流动的（单向数据流）")]),t._v(" "),s("p",[t._v("不管是父组件或是子组件都无法知道某个组件是有状态的还是无状态的，并且它们也并不关心它是函数组件还是 class 组件。")]),t._v(" "),s("p",[t._v("这就是为什么称 "),s("strong",[t._v("state 为局部的")]),t._v("或是封装的的原因。除了拥有并设置了它的组件，"),s("strong",[t._v("其他组件都无法访问")]),t._v("。")]),t._v(" "),s("p",[t._v("组件可以选择把它的 state 作为 props 向下传递到它的子组件中：")]),t._v(" "),s("div",{staticClass:"language-jsx line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-jsx"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("FormattedDate")])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("date")]),s("span",{pre:!0,attrs:{class:"token script language-javascript"}},[s("span",{pre:!0,attrs:{class:"token script-punctuation punctuation"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[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("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("date"),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")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[s("code",[t._v("FormattedDate")]),t._v(" 组件会在其 props 中接收参数 "),s("code",[t._v("date")]),t._v("，但是"),s("strong",[t._v("组件本身无法知道它是来自于 "),s("code",[t._v("Clock")]),t._v(" 的 state，或是 "),s("code",[t._v("Clock")]),t._v(" 的 props，还是手动输入的")]),t._v("。")]),t._v(" "),s("p",[t._v("这通常会被叫做“自上而下”或是**“单向”的数据流**。任何的 "),s("strong",[t._v("state 总是所属于特定的组件")]),t._v("，而且从该 state 派生的任何数据或 UI 只能影响树中“低于”它们的组件。")]),t._v(" "),s("p",[t._v("如果你把一个以组件构成的树想象成一个 props 的数据瀑布的话，那么每一个组件的 state 就像是在任意一点上给瀑布增加额外的水源，但是它只能向下流动。")]),t._v(" "),s("h4",{attrs:{id:"每个组件都是真正独立的。"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#每个组件都是真正独立的。"}},[t._v("#")]),t._v(" 每个组件都是真正独立的。")])])}),[],!1,null,null,null);s.default=e.exports}}]);