Prototype extension of the JavaScript array Traversal map ()

In JavaScript 1.6, JavaScript arrays add several useful methods: IndexOf, LastIndexOf, every, filter, ForEach, map, some, where the first two can be attributed to the element location method, Some of the latter can be categorized as iterative (iterative) methods.

Unfortunately, these new methods are not supported by all browsers, in which case we need to do it ourselves, and in these introductory articles we also provide implementations in browsers that do not support these new features.

The native methods are as follows:

1	varmappedArray = array.map(callback[, thisObject]);

• Callback: The callback function to execute for each array element.
• Thisobject: The This object that is defined when the callback function is executed. Venetian Macao Casino

Each element in an array executes one specified function (callback) at a time and creates a new array for the element with the result of each return. It executes the specified function only for non-empty elements in the array, no assignment, or the deleted element is ignored.

The callback function can have three parameters: the current element, the index of the current element, and the current array object. If the parameter thisobject is passed in, it will be treated as the this object inside the callback function (callback), and if it is not passed or null, the global object will be used.

Map does not change the original array, remember: Only the array elements passed in before the callback function executes, the elements that are added after the callback function begins execution are ignored, and when the callback function begins execution to the last element, the array element is deleted or changed, whichever time the callback function accesses the element. , the deleted element is ignored.

If the browser does not support the map method, you can also use prototype to expand it as follows:

01	<script type="text/javascript">

02

//扩展原型对象

03	Array.prototype.map = function(fn){

04	vara = [];

05	for(vari = 0; i < this.length; i++){

06	varvalue = fn(this[i], i);

07	if(value == null){

08	continue; //如果函数fn返回null，则从数组中删除该项

09

}

10	a.push(value);

11

}

12

returna;

13

};

14

15	//例子，arr为原始数组

16	vararr = [

17	{name: ‘gonn‘, age: 20, sex: ‘1‘, No: ‘274200‘},

18	{name: ‘nowamagic‘, age: 30, sex: ‘0‘, No: ‘274011‘},

19	{name: ‘frie‘, age: 40, sex: ‘1‘, No: ‘274212‘}

20

];

21

22	//使用map更改数组每项的值，可对数组每一项元素内部进行增删改，也可以通过return null来删除数组的某项

23	vararr2 = arr.map(function(item, i){

24	item.sex = item.sex == ‘0‘? ‘女‘: ‘男‘;

25	if(item.name == ‘tom‘){

26	returnnull; //删除name为tom的项

27

}

28

return{

29

index: i,

30	name: item.name,

31	age: item.age + 30 + i,

32	sex: item.sex

33

};

34

});

35

36	console.log(arr2);

37

</script>

In the Firefox firebug console output:

1

[

2	Object { index=0, name="gonn", age=50, 更多...},

3	Object { index=1, name="nowamagic", age=61, 更多...},

4	Object { index=2, name="frie", age=72, 更多...}

5

]

Or, you can extend it in the following ways:

View Source print?

01	if(!Array.prototype.map)

02

{

03	Array.prototype.map = function(fun /*, thisp*/)

04

{

05	varlen = this.length;

06	if(typeoffun != "function")

07	thrownewTypeError();

08

09	varres = newArray(len);

10	varthisp = arguments[1];

11	for(vari = 0; i < len; i++)

12

{

13	if(i inthis)

14	res[i] = fun.call(thisp, this[i], i, this);

15

}

16

17	returnres;

18

};

19

}

Happy Coding.

Prototype extension of the JavaScript array Traversal map ()