Modify array data header and tail push (), pop (), and Unshift (), Shift ()

1, push (), pop () and Unshift (), Shift ()

These two groups operate as an array, and change the length and content of the arrays themselves.

The difference is that push (), pop () is added or subtracted from the end of the array, Unshift (), and Shift () are added or subtracted from the head of the array.

Vararr = [1, 2];

2. Push () and unshift ()

adds several elements to the tail/head of the array and returns the new length of the array;

Arr.push (3,4);//Returns the new length of arr 4

arr; arr = [1,2,3,4];

Arr.unshift (0,0.5); Returns the new length of arr 6

arr; arr = [0,0.5,1,2,3,4];

3, Pop () and Shift ()

Delete 1 elements from the end/head of the array (delete only 1)and return the deleted elements ; empty array is to continue to delete, not error, but return undefined;

Arr.pop (); Returns 4;

arr; arr = [0,0.5,1,2,3];

Arr.pop (); Returns 3;

arr; arr = [0,0.5,1,2];

Arr.shift ();//return 0;

arr; arr = [0.5,1,2]

　　PS: pop () and shift () do not accept the parameter, even if the parameters are not egg use ~ ~;

Arr.pop (3); return 2; return to the last one forever;

arr; arr = [0.5,1];

Arr.shift (1); Returns 0.5; return to the first one forever;

arr; arr = [1];

Arr.pop (); returns 1;

arr; arr = [];

Arr.shift ()//return undefined;

arr; arr = [];

Modify array data header and tail push (), pop (), and Unshift (), Shift ()