(window.webpackJsonp=window.webpackJsonp||[]).push([[68],{791:function(t,s,a){"use strict";a.r(s);var n=a(20),e=Object(n.a)({},(function(){var t=this,s=t.$createElement,a=t._self._c||s;return a("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[a("h1",{attrs:{id:"模版字面量类型"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#模版字面量类型"}},[t._v("#")]),t._v(" 模版字面量类型")]),t._v(" "),a("blockquote",[a("p",[t._v("从 TypeScript 4.1 开始支持")])]),t._v(" "),a("p",[t._v("模版字面量类型以"),a("RouterLink",{attrs:{to:"/download/zh/handbook/literal-types.html"}},[t._v("字符串字面量类型")]),t._v("为基础，且可以展开为多个字符串类型的联合类型。")],1),t._v(" "),a("p",[t._v("其语法与 "),a("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals",target:"_blank",rel:"noopener noreferrer"}},[t._v("JavaScript 中的模版字面量"),a("OutboundLink")],1),t._v("是一致的，但是是用在类型的位置上。\n当与某个具体的字面量类型一起使用时，模版字面量会将文本连接从而生成一个新的字符串字面量类型。")]),t._v(" "),a("div",{staticClass:"language-ts 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"),a("p",[t._v("例如，JavaScript 中有一个常见的模式是基于对象的现有属性来扩展它。\n下面我们定义一个函数类型 "),a("code",[t._v("on")]),t._v(" ，它用于监听值的变化。")]),t._v(" "),a("div",{staticClass:"language-ts extra-class"},[a("pre",{pre:!0,attrs:{class:"language-ts"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("declare")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("makeWatchedObject")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("obj"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("any")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("any")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])])]),a("p",[t._v("注意， "),a("code",[t._v("on")]),t._v("  会监听 "),a("code",[t._v('"firstNameChanged"')]),t._v("  事件，而不是 "),a("code",[t._v('"firstName"')]),t._v(" 。\n模版字面量提供了操作字符串类型的能力：")]),t._v(" "),a("div",{staticClass:"language-ts extra-class"},[a("pre",{pre:!0,attrs:{class:"language-ts"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("type")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("PropEventSource"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("Type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    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punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/// Create a \"watched object\" with an 'on' method")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/// so that you can watch for changes to properties.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("declare")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token generic-function"}},[a("span",{pre:!0,attrs:{class:"token function"}},[t._v("makeWatchedObject")]),a("span",{pre:!0,attrs:{class:"token generic class-name"}},[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("Type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("\n    obj"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" Type\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" Type "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" PropEventSource"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("Type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])])]),a("p",[t._v("这样做之后，当传入了错误的属性名会产生一个错误：")]),t._v(" "),a("div",{staticClass:"language-ts extra-class"},[a("pre",{pre:!0,attrs:{class:"language-ts"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("type")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("PropEventSource"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("Type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])]),t._v(" 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"),a("span",{pre:!0,attrs:{class:"token constant"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[t._v("T")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" PropEventSource"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token constant"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" person "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("makeWatchedObject")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    firstName"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Saoirse'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n    lastName"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Ronan'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n    age"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("26")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nperson"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("on")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'firstNameChanged'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=>")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 以下存在拼写错误")]),t._v("\nperson"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("on")]),a("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=>")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])])]),a("h3",{attrs:{id:"模版字面量类型推断"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#模版字面量类型推断"}},[t._v("#")]),t._v(" 模版字面量类型推断")]),t._v(" "),a("p",[t._v("注意，上例中没有使用原属性值的类型，在回调函数中仍使用 "),a("code",[t._v("any")]),t._v("  类型。\n模版字面量类型能够从替换字符串的位置推断出类型。")]),t._v(" "),a("p",[t._v("下面，我们将上例修改成泛型，它会从 "),a("code",[t._v("eventName")]),t._v("  字符串来推断出属性名。")]),t._v(" "),a("div",{staticClass:"language-ts 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