JS Array knowledge

Shift: Deletes the first item of the original array and returns the value of the deleted element; returns undefined if the array is empty

JavaScript code

1. var a = [1,2,3,4,5];
2. 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

JavaScript code

1. var a = [1,2,3,4,5];
2. 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 Test return value is 7, so the return value of this method is not reliable, need to use the return value when the splice can be used instead of this method.
Pop: Deletes the last item of the original array and returns the value of the deleted element; returns undefined if the array is empty

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = A.pop (); //a:[1,2,3,4] B:5

Push: Adds a parameter to the end of the original array and returns the length of the array

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = A.push (6,7); //a:[1,2,3,4,5,6,7] B:7

Concat: Returns a new array that consists of adding parameters to the original array

JavaScript code

1. var a = [1,2,3,4,5];
2. 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 item from the start position and inserts val1,val2 from that position,...

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = A.splice (2,2,7,8,9); //a:[1,2,7,8,9,5] b:[3,4]
3. var B = a.splice (0,1); //With Shift
4. A.splice (0,0,-2,-1); var b = a.length; //with unshift
5. var B = A.splice (a.length-1,1); //with pop
6. A.splice (a.length,0,6,7); var b = a.length; //with push

Reverse: Reverse the array

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = A.reverse (); //a:[5,4,3,2,1] b:[5,4,3,2,1]

Sort (orderfunction): Sorts the array by the specified parameters

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = A.sort (); //a:[1,2,3,4,5] b:[1,2,3,4,5]

Slice (Start,end): Returns a new array that consists of the entries from the original array that specify the starting subscript to the end subscript

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = a.slice (2,5); //a:[1,2,3,4,5] b:[3,4,5]

Join (Separator): Sets the element group of the array as a string, separator as a delimiter, or by default with a comma delimiter if omitted

JavaScript code

1. var a = [1,2,3,4,5];
2. var B = a.join ("|"); //a:[1,2,3,4,5] B: "1|2|3|4|5"

An array is an internal object provided by JavaScript, which is a standard set of elements that we can add (push), delete (shift) inside, and we can also iterate through the elements in a for loop, so can we have other collections in JavaScript besides arrays?
Because of the language nature of JavaScript, we can add and remove properties to common objects dynamically. So object can also be seen as a special set of JS. The following compares the attributes of array and object:

JavaScript code

2. 　　Array:
6. /* NEW: */var ary = new Array (), or var ary = [];
8. /* Add: */ary.push (value);
10. /* Delete: */deleteary[n];
12. /* Traversal: */for ( var i=0; i < ary.length; ++i) ary[i];
16. 　　Object:
20. /* NEW: */var obj = new Object (); or var obj = {};
22. /* Add: */obj[key] = value; (Key is String)
24. /* Delete: */deleteObj[key];
26. /* Traversal: */for ( var key in obj) Obj[key];

Reproduced........................

JS Array knowledge