JavaScript arrays about 3

The first two sections say the basics of creating arrays, queue methods, sorting, and some operation methods, and this section is about iterative and merging methods.

　　　　Every () method & Some () method

These two methods run the given function for each item in the array, and then return a Boolean value that can be understood as the difference between everyone and someone, and look at an example:

vararr=[1,2,3,4,5];vareveryresult=arr.every (function (Item,index,arr) {return(item>2); })        //falsevarsomeresult=arr.some (function (Item,index,arr) {return(item>2); })        //true

All two methods execute a function, the first parameter of the function represents each array element of the iteration, the second parameter represents the subscript, and the third parameter represents the array.

　　　Filter () method

1 var arr=[1,2,3,4,5]2var filterresult=arr.filter (function(item, Index,arr) {3        return (item>2)4 })    //[ 3,4,5]

The method executes the given function for each item in the array, and returns a set of items that the function returns True.

　　　　Map () Method & ForEach () method

Map () returns an array of the results of each function call, and ForEach () does not return a value.

1 vararr=[1,2,3,4,5]2 varMapresult=arr.map (function(Item,index,arr) {3        returnItem*24})//[2,4,6,8,10]5 varForresult=arr.foreach (function(Item,index,arr) {6        //perform some actions7})//undefined

ForEach () is essentially the same as using a for loop to iterate over an algebraic group.

　　　　Reduce () method & Reduceright () method

1 var arr=[1,2,3]; 2 arr.reduce (function(x,y,index,arr) {34       return x+  Y5 },0);    // 6

Both methods have two parameters, the first is a callback function to execute, and the second represents the initial value to be used as the basis for the merge (optional).

　　　IndexOf () Method & LastIndexOf ()

1 var arr=[1,2,3,4,5]; 2 arr.indexof (1,-1);    // -1 3 arr.lastindexof (1,-1)    //0

Receives two parameters, the first represents the element to find, the second represents the start position, and if any, returns the position of the element in the array subscript, No 1

The array is probably summed up so much, at the same time the array is also the object, will later in the object's learning summary to explore.

JavaScript arrays about 3