js的官方文檔網站：

https://developer.mozilla.org/

js版本介紹的文章：

https://www.w3schools.com/js/js_versions.asp

toString()用法：

想在html里面使用最新的js版本：

https://developer.mozilla.org/en-US/docs/Archive/Web/JavaScript/New_in_JavaScript/1.8

Wikipedia (or rather, the community on Wikipedia) keeps a pretty good up-to-date list here.

Most browsers are on 1.5 (though they have features of later versions)
Mozilla progresses with every dot release (they maintain the standard so that's not surprising)
Firefox 4 is on JavaScript 1.8.5
The other big off-the-beaten-path one is IE9 - it implements ECMAScript 5, but doesn't implement all the features of JavaScript 1.8.5 (not sure what they're calling this version of JScript, engine codenamed Chakra, yet).

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查看各個瀏覽器的javascript版本的方法:

https://stackoverflow.com/questions/4271566/how-do-i-know-which-version-of-javascript-im-using

新建一個html頁面，用各個瀏覽器打開即可：

<script type="text/javascript">
  var jsver = 1.0;
</script>
<script language="Javascript1.1">
  jsver = 1.1;
</script>
<script language="Javascript1.2">
  jsver = 1.2;
</script>
<script language="Javascript1.3">
  jsver = 1.3;
</script>
<script language="Javascript1.4">
  jsver = 1.4;
</script>
<script language="Javascript1.5">
  jsver = 1.5;
</script>
<script language="Javascript1.6">
  jsver = 1.6;
</script>
<script language="Javascript1.7">
  jsver = 1.7;
</script>
<script language="Javascript1.8">
  jsver = 1.8;
</script>
<script language="Javascript1.9">
  jsver = 1.9;
</script>

<script type="text/javascript">
  alert(jsver);
</script>

1. chrome: