Google Closure Tools developer Google
Google Closure Tools is a set of tools to help developers build rich web applications with JavaScript. It was developed by Google for use in their web applications such as Gmail, Google Docs and Google Maps.Closure Compiler
The Closure Compiler is a tool for making JavaScript downloads run faster, at the expense of human readability. It does not compile from JavaScript to machine code, but rather compiles from JavaScript to more efficient JavaScript.   
It parses JavaScript, analyzes it, removes dead code and rewrites and minifies what is left. It also checks syntax, variable references, and types and warns about common JavaScript pitfalls. It supports transpiling modern ECMAScript code to ECMAScript 5, so that programmers can write JavaScript that uses those features, and run it in browsers or other environments that do not yet support them. (the Traceur Compiler is another Google project that supports transpiling ES6 to ES3.)
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