History of Array.prototype.forEach()

Minor nit picking to make closer to other examples

If the array is modified during iteration, other elements might be skipped

clr review

The optional this in the Syntax example should go after the brackets. Please see https://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.20

The optional comma in the Syntax example should be inside the brackets. Please see: https://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.20

clear review

Polyfill: use '===' for null comparison