A detailed example of the new array method in ECMASCRIPT5

The ECMASCRIPT5 Standard, released on December 3, 2009, brings some new ways to improve the operation of existing array arrays. (Note compatibility)

In ES5, a total of 9 array methods: http://kangax.github.io/compat-table/es5/

Array.prototype.indexofarray.prototype.lastindexofarray.prototype.everyarray.prototype.somearray.prototype.foreacharray.p Rototype.mapArray.prototype.filterArray.prototype.reduceArray.prototype.reduceRight

Here are 7 methods, the first 5 methods are common, many developers will use:

1, IndexOf ()

The IndexOf () method returns the position of the first element found in the array, or 1 if it does not exist.

vararr = [' Apple ', ' orange ', ' pear '], found=false;//not used for(vari = 0, L = arr.length; I < L; i++) {    if(Arr[i] = = = ' Orange ') {found=true; }}console.log ("Found:", found);//==> found:true//after useConsole.log ("Found:", Arr.indexof ("orange")! =-1);//==> found:true

2. Filter ()

The filter () method creates an array of new matching filter conditions.

When no filter () is used:

var arr=[{"name": "Apple", "Count": 2},{"name": "Orange", "Count": 5},{"name": " Pear "," Count ": 3},{" name ":" Orange "," count ": +},]var newArr = [];  for (var i = 0; i < arr.length; i++) {    if (arr[i].name = = = "Orange") {        NEWARR . push (Arr[i]);}    } Console.log ("Filter results:", NEWARR);

The filter () is used:

var newArr = Arr.filter (function(item) {    return item.name = = = "Orange";});
Console.log ("Filter results:", NEWARR);

3. ForEach ()

foreach executes the corresponding method for each element, which is used to replace the for loop.

var arr = [1, 2, 3, 4, 5, 6, 7, 8]; // using A For loop  for (var i = 0, L = arr.length; i < L; i++) {    console.log (arr[i]);} // Use the ForEach loop Arr.foreach (function(item, index) {    console.log (item);});

4. Map ()

Map () After each element of the array is manipulated (mapped), a new array is returned.

varOldarr =[{first_name:"Colin", last_name:"Toh"}, {first_name:"Addy", last_name:"Osmani"}, {first_name:"Yehuda", last_name:"Katz"}];
functionGetnewarr () {varNEWARR = [];  for(vari = 0; i < oldarr.length; i++) {        varitem =Oldarr[i]; Item.full_name= [Item.first_name, Item.last_name].join (""); Newarr[i]=item; }    returnNEWARR;}varPersonName =Getnewarr ();p Ersonname.foreach (function(item, index) {console.log (item);})/** * * output: Object {first_name: "Colin", Last_Name: "Toh", Full_name: "Colin Toh"}object {first_name: "Addy", last_name: "Osmani", Full_name: "Addy Osmani"}object {first_name: "Yehuda", Last_Name: "Katz", Full_name: "Yehuda Katz"}****/

Use the Map () method:

functionGetnewarr () {returnOldarr.map (function(item, index) {item.full_name= [Item.first_name, Item.last_name].join (""); returnitem; })}varPersonName =Getnewarr ();p Ersonname.foreach (function(item, index) {console.log (item);})/** * * output: Object {first_name: "Colin", Last_Name: "Toh", Full_name: "Colin Toh"}object {first_name: "Addy", last_name: "Osmani", Full_name: "Addy Osmani"}object {first_name: "Yehuda", Last_Name: "Katz", Full_name: "Yehuda Katz"}****/

5. Reduce ()

Reduce () can implement the function of an accumulator, lowering each value (from left to right) of the array to a value. It can also be understood as: Let the preceding and latter in the array do some kind of operation, and accumulate the final value;

Scene: Count the number of non-repeating words in an array;

 var  arr = ["Apple", "orange", "apple", "orange", "pear", "orange" ]; function   getwordcnt () { var  obj = {};  for  (var  i = 0; i < arr.length; i+ + var  item = Arr[i]; Obj[item]  = (Obj[item] + 1) | |    1 return   obj; Console.log (getwordcnt ());  //  output result:  //  Object {apple:2, orange:3, pear:1}  

After using reduce ():

var arr = ["Apple", "orange", "apple", "orange", "pear", "orange"]; function getwordcnt () {    return arr.reduce (function(prev, next) {        = (Prev[next] + 1 ) || 1;         return prev;    }, {});} Console.log (getwordcnt ()); // Output Result: // Object {apple:2, orange:3, pear:1}

6, Array.some (callback[, Thisobject]); callback: functions are used to test certain elements. Thisobject: The object is used as the execution callback.

Detects if there are certain items in the array that meet the criteria;

var = [scores, max, +, +---]; var current =; function passed (score) {    return score >//  = = > True

7, Array.every (callback[, Thisobject]); callback: The function is used to test each element. Thisobject: The object is used as the execution callback.

Detects whether each item in the array meets the criteria;

var = [scores, max, +, +---]; var current =; function passed (score) {    return score >//  = = > False

A detailed example of the new array method in ECMASCRIPT5