ES6 Chapter 1

• Transpiling
  • [?] backwards compatibility OR rapid evolvement
  • [Answer] transformation compiling: to transform your ES6 code into equivalent (or close) matches that work in ES5 environments. (transformations how/when linting, minification, etc)

  • [Example] For example, consider shorthand property definitions

              var foo = [1,2,3];
              var obj = {
                  foo 	// means `foo: foo`
              };
              obj.foo;
              // [1,2,3]
    
              -------------------------------
              // transpiles:
    
              var foo = [1,2,3];
              var obj = {
                  foo: foo
              };
              obj.foo;
              // [1,2,3]
    

Not all new ES6 features need a transpiler. Polyfills (aka shims) are a pattern for defining equivalent behavior from a newer environment into an older environment.

				// strict equality of two values
				// without the nuanced exceptions that === has for NaN and -0 values
				if (!Object.is) {
					Object.is = function(v1, v2) {
					
					// test for `-0`
					if (v1 === 0 && v2 === 0) {
						return 1 / v1 === 1 / v2;
					}
					
					// test for `NaN`
					if (v1 !== v1) {
						return v2 !== v2;
					}
					
					// everything else
						return v1 === v2;
					};
				}