ECMAScript is the scripting language standardized by Ecma International in the ECMA-262 specification and ISO/IEC 16262. The language is widely used for client-side scripting on the web, in the form of several well-known dialects such as JavaScript, JScript, and ActionScript.
Depends on you, but I think most commonly used for web dev is JavaScript
JavaScript was formalized in the ECMAScript language standard and is primarily used in the form of client-side JavaScript
I would recommend this book
By learning more and more about the language itself and writing tests
Look here
