ECMAScript 5
The last most important milestone in ECMAScript revisions was ECMAScript 5 (ES5), officially accepted in December 2009. ECMAScript 5 standard is implemented and supported on all major browsers and server-side technologies.
ES5 was a major revision because apart from several important syntactic changes and additions to the standard libraries, ES5 also introduced several new constructs in the language.
For instance, ES5 introduced 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 will declare your intention using (once per function, or ...
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