ECMAScript 5 defines nine new array methods for iterating, mapping, filtering, testing, reducing, and searching arrays. The subsections below describe these methods.
Before we cover the details, however, it is worth making some
generalizations about these ECMAScript 5 array methods. First, most of
the methods accept a function as their first argument and invoke that
function once for each element (or some elements) of the array. If the
array is sparse, the function you pass is not invoked for nonexistent
elements. In most cases, the function you supply is invoked with three
arguments: the value of the array element, the index of the array
element, and the array itself. Often, you only need the first of these
argument values and can ignore the second and third values. Most of
the ECMAScript 5 array methods that accept a function as their first
argument accept an optional second argument. If specified, the
function is invoked as if it is a method of this second argument. That
is, the second argument you pass becomes the value of the
this keyword inside of the function you
pass. The return value of the function you pass is important, but
different methods handle the return value in different ways. None of
the ECMAScript 5 array methods modify the array on which they are
invoked. If you pass a function to these methods, that function may
modify the array, of course.
forEach() method iterates through an array, invoking a function you specify for ...