javascript - 如何检查字符串“ StartsWith”是否为另一个字符串？(How to check if a string “StartsWith” another string?)

Question

How would I write the equivalent of C#'s String.StartsWith in JavaScript?

(如何在JavaScript中编写等效于C＃的String.StartsWith ？)

var haystack = 'hello world';
var needle = 'he';

haystack.startsWith(needle) == true

Note: This is an old question, and as pointed out in the comments ECMAScript 2015 (ES6) introduced the .startsWith method.

(注意：这是一个古老的问题，正如注释中指出的那样，ECMAScript 2015（ES6）引入了.startsWith方法。)

However, at the time of writing this update (2015) browser support is far from complete .

(但是，在撰写此更新（2015）时， 浏览器支持还远远没有完成 。)

  ask by translate from so

Answer 1

You can use ECMAScript 6's String.prototype.startsWith() method, but it's not yet supported in all browsers .

(您可以使用ECMAScript 6的String.prototype.startsWith()方法，但并非所有浏览器都支持该方法 。)

You'll want to use a shim/polyfill to add it on browsers that don't support it.

(您将需要使用填充程序/填充来将其添加到不支持它的浏览器中。)

Creating an implementation that complies with all the details laid out in the spec is a little complicated.

(创建一个符合规范中所有细节的实现会有些复杂。)

If you want a faithful shim, use either:

(如果您想要忠实的垫片，请使用以下任一方法：)

• Matthias Bynens's String.prototype.startsWith shim , or

  (Matthias Bynens的String.prototype.startsWith shim ，或者)

• The es6-shim , which shims as much of the ES6 spec as possible, including String.prototype.startsWith .

  (es6-shim ，它尽可能多地影响ES6规范，包括String.prototype.startsWith 。)

Once you've shimmed the method (or if you're only supporting browsers and JavaScript engines that already have it), you can use it like this:

(对方法进行填充后（或者如果您仅支持已拥有该方法的浏览器和JavaScript引擎），则可以按以下方式使用它：)

"Hello World!".startsWith("He"); // true

var haystack = "Hello world";
var prefix = 'orl';
haystack.startsWith(prefix); // false