ECMAscript5 new in-array functions

IndexOf ()
Format: Array. indexOf (item, start)
Function: Starting with the subscript, look for the item in the array for the first occurrence of the subscript.
Parameter: Item We're going to find the element
Start from which subscript to search, if not, the default starting from 0 to find
Return value: 1 not found
>=0 found the subscript.

var arr = ["Batman", "Superman", "Flash", "Green Lantern", "Wonder Woman", "Green Lantern"); var res = Arr.indexof ("Green Lantern", 4); alert (res); // 5 var arr = ["Batman", "Superman", "Flash", "Green Lantern", "Wonder Woman", "Green Lantern"); var res = indexOf (arr, "green" SSS); alert (res); // -1  not found

Custom (self-encapsulated function) indexOf

function indexOf (arr, item, start) {        var index =-1;   Suppose you can't find the        if(!  Start) {            = 0;        }      for (var i = start; i < arr.length; i++) {        if(arr[i] = = = Item            ) {=< c20> i;              Break ;        }    }     return index;}        

. ForEach (function (item, index, arr) {})

ForEach ()
Format: Array. ForEach (function (item, index, arr) {
Item currently traversed to the element
Index currently traversed by the element subscript
The current array of arr itself
})
Function: Used to iterate through an array.

For loop
For...in
Foreach

var arr = ["Batman", "Superman", "Flash", "Green Lantern", "Wonder Woman", "Green Lantern"];arr.foreach (function+ "," +  index);})

Effect:

Traditional way

 for (var i = 0; i < arr.length; i++) {alert (arr[i]);}

Map () traversal

var arr = [Ten, +, +, +]; var newArr = Arr.map (function(item, index, arr) {  return//  Newarr the result of the subscript }) alert (arr); // Ten, +, (NEWARR); // 13,26 ,-------

Filter () Filtering

  var arr = [Ten, +, +, +]; var newArr = Arr.filter (Item, index, arr) {  // finds all elements greater than 20 in the original array, Generate a new array return// filter Condition }); alert (arr); // Ten, +, (NEWARR); // it's A.　　

/*
Some () some

Determine if there are elements that meet the criteria.

Note: Simply exit the loop as soon as you find the first element that meets the criteria.
Return value: True False

var arr = [Ten, +, +, +]; var res = arr.some (function(item, index, arr) {    //  Alert (item + "," + index);     // conditions of judgment.     return item >;}) Alert (res); // it's A.

Every ()
Determines whether all elements meet the criteria.

"Note" To find the first element that does not meet the criteria, terminate the loop and return False

Return value: True False

var arr = [Ten, +, +, +]; var res = arr.every (function(item, index, arr) {    + "," + index ")    ; // judge the condition.     return item <;}) Alert (res); // false

Modify the judging conditions in the above code to:

return item > 5;

The result is true:

Alert (res); // true

Reduce () Merge

Syntax: array. reduce (function (prev, next, index, arr) {})

Prev The result of an expression after the last loop return
Next the element that is traversed
Index this time the subscript of the traversed element

var arr = [Ten, +, +, +]; var res = arr.reduce (function(prev, Next, index, arr) {/*prev Last loop　　Return the result of the expression after next this time traversing the element index this time traversing the subscript of the element */+ "," + Next ";  return prev + Next;}) Alert (res); // 150 The sum of the array elements is realized by this method

ECMAscript5 new in-array functions