As with most programming languages, ECMAScript has evolved over time. It was initially developed in the mid-nineties for use in client-side scripting. The current standard is ECMAScript 5; however, Version 6 is currently being worked on. The TypeScript compiler provides a list of options to change the way your code is generated. In this section, we will look at these options and compare the results.
Writing JavaScript code means your code must be portable across multiple types of client devices and browsers. You may be forced to not only support the latest version of a browser but potentially any of its previous versions. For this reason, the compiler supports compiling your TypeScript code into different versions of ECMAScript. ECMAScript 3 was a widely adopted and heavily used standard and has survived in many legacy browsers. ECMAScript 4 was abandoned when the group responsible for creating the standard could not agree on the language features...