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"),t("p",[s._v("除了注释，装饰器还能用来类型检查。所以，对于类来说，这项功能相当有用。从长期来看，它将是 JavaScript 代码静态分析的重要工具。")]),s._v(" "),t("h2",{attrs:{id:"为什么装饰器不能用于函数"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#为什么装饰器不能用于函数"}},[s._v("#")]),s._v(" 为什么装饰器不能用于函数？")]),s._v(" "),t("p",[s._v("装饰器只能用于类和类的方法，不能用于函数，因为存在函数提升。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("var")]),s._v(" counter "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("var")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("add")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token 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"),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br")])]),t("p",[s._v("下面是另一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("var")]),s._v(" readOnly 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"),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("上面代码也有问题，因为实际执行是下面这样。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("var")]),s._v(" readOnly"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n@readOnly\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" 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