为什么在Chrome中未定义String.toLowerCase但在Firefox中未定义？

Question

In the Chrome console, String.toLowerCase returns undefined. However in Firefox, it does not.

What's the reason for the difference?

 var body = $("body"); body.append(new String(String.toLowerCase).toString()); body.append("<br>"); body.append(String.prototype.toLowerCase.toString()); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 

Answer 1

String.toLowerCase is one of the Generics that Firefox has allowed for String, Array (and possibly other). They are not defined in any ECMAScript standard and are considered deprecated by Firefox and will be removed.

Extracted from the MDN docs :

String generics are non-standard, deprecated and will get removed near future. Note that you can not rely on them cross-browser without using the shim that is provided below.

See also:

• Introduction of Generics in Firefox's JS 1.6
• Deprecation announcement (Not sure how much support the site has from Mozilla, so take this one with a grain of salt.)
• Deprecation warning implementation ticket

Answer 2

Is this what you are trying to do? Either of these work fine in chrome for me.

 let body = $("body"); let str = 'STRING TO LOWER'; body.append(str.toLowerCase()); body.append("<br>"); body.append("ALL CAPS".toLowerCase()); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>