ECMAScript 5
Revision 3 of ECMAScript is the one you can take for granted to be implemented in all browsers and environments. Revision 4 was skipped and revision 5 (let's call it ES5 for short) was officially accepted in December 2009.
ES5 introduces some new objects and properties and also the so-called "strict mode". Strict mode is a subset of the language that excludes deprecated features. The strict mode is opt-in and not required, meaning that if you want your code to run in the strict mode, you declare your intention using (once per function, or once for the whole program) the following string:
"use strict";
This is just a JavaScript string, and it's OK to have strings floating around unassigned to any variable. As a result, older browsers ...
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