JavaScript Array method Rollup

JS array elements to add and delete has been more puzzled, summed up as follows:
var arr = new Array ();
Arr[0] = "AAA";
ARR[1] = "BBB";
ARR[2] = "CCC";
alert (arr.length);//3
Arr.pop ();
alert (arr.length);//2
Alert (arr[arr.length-1]);//bbb
Arr.pop ();
Alert (arr[arr.length-1]);//aaa
alert (arr.length);//1

var arr2 = new Array ();
alert (arr2.length);//0
Arr2[0] = "AAA";
ARR2[1] = "BBB";
alert (arr2.length);//2
Arr2.pop ();
alert (arr2.length);//1
ARR2 = Arr2.slice (0,arr2.length-1);
alert (arr2.length);//0
Arr2[0] = "AAA";
ARR2[1] = "BBB";
ARR2[2] = "CCC";
ARR2 = Arr2.slice (0,1);
alert (arr2.length);//1
Alert (arr2[0]);//aaa
Alert (arr2[1]);//undefined

Shift: Deletes the first item of the original array and returns the value of the deleted element, or returns undefined if the array is empty
var a = [1,2,3,4,5];
var B = A.shift (); a:[2,3,4,5] B:1

Unshift: Adds a parameter to the beginning of the original array and returns the length of the array
var a = [1,2,3,4,5];
var B = A.unshift ( -2,-1); a:[-2,-1,1,2,3,4,5] B:7
Note: The test return value under IE6.0 is always undefined,ff2.0 the test return value is 7, so the return value of this method is unreliable, and it is necessary to use splice instead of this method with the return value.

Pop: Deletes the last item of the original array and returns the value of the deleted element, or returns undefined if the array is empty
var a = [1,2,3,4,5];
var B = A.pop (); a:[1,2,3,4] B:5//No need to return the words directly call it

Push: Adds a parameter to the end of the original array and returns the length of the array
var a = [1,2,3,4,5];
var B = A.push (6,7); a:[1,2,3,4,5,6,7] B:7

Concat: Returns a new array that adds a parameter to the original array.
var a = [1,2,3,4,5];
var B = A.concat (6,7); a:[1,2,3,4,5] b:[1,2,3,4,5,6,7]

Splice (Start,deletecount,val1,val2,...) : Deletes the DeleteCount entry from the start position and inserts the Val1,val2 from that location,...
var a = [1,2,3,4,5];
var B = A.splice (2,2,7,8,9); a:[1,2,7,8,9,5] b:[3,4]
var B = a.splice (0,1); With shift
A.splice (0,0,-2,-1); var B = a.length; With Unshift
var B = A.splice (a.length-1,1); Same pop
A.splice (a.length,0,6,7); var B = a.length; Same push

Reverse: Reverse-order the array
var a = [1,2,3,4,5];
var B = A.reverse (); a:[5,4,3,2,1] b:[5,4,3,2,1]

Sort (orderfunction): Sorting by specified array of parameters
var a = [1,2,3,4,5];
var B = A.sort (); a:[1,2,3,4,5] b:[1,2,3,4,5]

Slice (Start,end): Returns a new array of items from the original array specifying the start subscript to the end subscript
var a = [1,2,3,4,5];
var B = a.slice (2,5); a:[1,2,3,4,5] b:[3,4,5]

Join (Separator): Sets the element of an array to a string, separator as a delimiter, and omitted by default with a comma as the delimiter
var a = [1,2,3,4,5];
var B = A.join (""); a:[1,2,3,4,5] B: "12345"