blocks|key|4056569|text|padStart是在ES2017标准中定义的。您需要告诉typescript使用适当的类型(用于ES2017的类型)。如果您的运行时支持ES2017所需的所有语言特性，则可以通过将目标设置为ES2017来实现这一点(在编写本文时，情况可能并非如此)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4056570|另一种选择是只设置libs选项，以便根据ES2017获得运行时对象的类型，但仍然向下编译到目标语言版本。(请注意，运行时本身需要支持padStart，typescript将不提供任何多边形填充)|4056571|您可以使用lib选项在tsconfig中执行此操作：|4056572|"compilerOptions":+{
++++"target":+"es2016",
++++"lib":+[
++++++++"es2017",
++++++++"dom"
++++++++"scripthost"
++++],
++++//+...

}|code-block|syntax|javascript|4056573|您可以在这个answer中阅读更多关于lib+vs+target的内容。|4056574|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/51043439/using-latest-javascript-features-in-typescript-such-as-es2018/51044240#51044240^0|0|8|A|6|1C|6|1W|6|2N|6|0|9|4|K|6|1U|8|0|5|3|B|8|0|0|6|6|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1G|8|@$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1L|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1M|8|@]|D|@$9|1N|A|1O|1|1P]]|E|$]]|$1|Q|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

<code>padStart</code> is defined in the <code>ES2017</code> standard. You need to tell typescript to use the apropriate typings (the ones for <code>ES2017</code>). You can do this either by setting the target to <code>ES2017</code>, if your runtime supports all the language features required by <code>ES2017</code> (which is probably not the case at the time of writing). 

Another option is to just set the <code>libs</code> option in order to get the typings for runtime objects in accordance with <code>ES2017</code> but still compile down to whatever language version you are targeting.(Note that the runtime itself needs to support <code>padStart</code>, typescript will not provide any poly-fills)

You can do this in <code>tsconfig</code> using the <code>lib</code> option:

<pre><code>"compilerOptions": {
 "target": "es2016",
 "lib": [
 "es2017",
 "dom"
 "scripthost"
 ],
 // ...

}
</code></pre>

You can read more about lib vs target in this <a href="https://stackoverflow.com/questions/51043439/using-latest-javascript-features-in-typescript-such-as-es2018/51044240#51044240">answer</a>

blocks|key|4055877|text|要使TypeScript能够识别String.prototype.padStart()，您需要在tsconfig.json的库列表中指定es2017。如果你这样做了，那么TypeScript将假设所有的ES2017特性都可以使用，而这可能不是你想要的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4055878|像Node.js这样的平台并不总是实现新的ECMAScript语言规范的完整特性集，所以只添加您确信存在的语言特性会更安全。如果您不确定目标平台支持哪些功能，可以在node.green或MDNs+browser+compatibility+list等页面上查找。|4055879|padStart函数是字符串原型的一部分，因此只需在tsconfig.json中添加es2017.string就足够了|4055880|{
++"compilerOptions":+{
++++"lib":+["es6",+"es2017.string"],
++++...
++},
}|code-block|syntax|javascript|4055881|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart|1|https://node.green/#ES2017|2|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart#Browser_compatibility^0|1C|D|1W|6|G|R|0|0|2A|A|1|2L|V|2|0|0|8|Q|D|16|D|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]]|E|$]]|$1|F|3|G|5|6|7|18|8|@]|D|@$9|19|A|1A|1|1B]|$9|1C|A|1D|1|1E]]|E|$]]|$1|H|3|I|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1M|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|1N|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]|Y|$5|R|S|T|E|$U|Z]]]]

To make TypeScript aware of <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart" rel="noreferrer">String.prototype.padStart()</a>, you need to specify <code>es2017</code> in the list of libraries in your <code>tsconfig.json</code>. If you do that, then TypeScript will assume that all the ES2017 features can be used which might not be exactly what you want. 

Platforms like Node.js don't always implement the complete feature set of a new ECMAScript language specification, so it's safer to only add the language features where you are confident that they exist. If you are not sure which features are supported by your targeted platform, you can look them up on pages likes <a href="https://node.green/#ES2017" rel="noreferrer">node.green</a> or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart#Browser_compatibility" rel="noreferrer">MDNs browser compatibility list</a>.

The <code>padStart</code> function is part of the String prototype, so it is sufficient to just add <code>es2017.string</code> in your <code>tsconfig.json</code>:

<pre><code>{
 "compilerOptions": {
 "lib": ["es6", "es2017.string"],
 ...
 },
}
</code></pre>

When I type in the chrome dev tools:

<pre><code>"1".padStart(2,0)
</code></pre>

I get 

<pre><code>"01"
</code></pre>

But when I write 

<pre><code>"1".padStart(2,0)
</code></pre>

in my typescript project

I get

<pre><code>Property 'padStart' does not exist on type 'string'.
</code></pre>

Why does Typescript complain? How do I fix this?

Typescript tells me property 'padStart' does not exist on type 'string'. Why?

当我输入chrome dev工具时："1".padStart(2,0)我得到了"01"但是当我写的时候"1".padStart(2,0)在我的typescript项目中我得到了Property 'padStart' does not exist on type 'string'.为什么Typescript会抱怨？我该如...

问Typescript告诉我类型'string‘上不存在属性'padStart’。为什么？
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问Typescript告诉我类型'string‘上不存在属性'padStart’。为什么？
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