JS array-related knowledge

To create an array method one:

            var a1=New Array (5);            Console.log (a1.length); // 5            // [], the array is empty             var a2=new Array (5,6);            Console.log (a2.length); // 2            // [5,6]            

Create array Two:

           var a1=[5];            Console.log (a1.length); // 1            // [5]             var A2=[5,6];            Console.log (a2.length); // 2            // [5,6]    

Index and length of the array:

var a1=[1,2,3,4];console.log (a1[//1var i=1//2// 3

Console.log (1 in A1); // true, is indeed a property

           var a=New Array (+/-);            a[100]=100;             // 101            // undefined            // undefined            Console.log (a[100]); 100

In the example above:

Although direct to a[100] assignment does not affect a[4] or a[99], but the length of the array is affected, the array is equal to the maximum number of index+1 in the array, we know the length property of the array is also
is a writable property that, when forced to set the length property value of an array to be less than or equal to the maximum index value, the array automatically deletes data with indexd greater than or equal to length, appending a few sentences in the code just now

a.length=2Console.log (a); // [up]

A.length=5/ /// back No 3 undefined

Element additions/Deletions

            var a=New Array (+/-);            a[3]=4;            Console.log (a); // [1, 2, 3, 4]

           Delete a[2];            Console.log (a[//undefined

JS Stack method:

            var a=New Array (+/-);            A.push (4);            Console.log (a); //             Console.log (a.length);   4            Console.log (A.pop (a));   4            //            console.log (a.length);   3

The queue method of JS

            var a=New Array (+/-);            A.unshift (4);            Console.log (a); //             Console.log (a.length);   4            Console.log (A.shift (a));   4            //            console.log (a.length);   3

How to delete JS

            var a=New Array (1,2,3,4,5);            Console.log (A.splice (1,3)); //             Console.log (a.length);   2            Console.log (a);   [1,5]

The JS loop iterates through the array:

New Array (13.5,3,4,5,6);  for (Var i=0;i<arr.length;i++) {  alert (arr[i]);}

New Array () mycars[0] = "Saab"mycars[1] = "Volvo"mycars[2] = "BMW"for + "< br/> ")}

The conversion between JS array and string:

New Array (0,1,2,3,4= A.join ("-");

var s = "Abc,abcd,aaa"= S.split (","); // decompose at each comma (,). 

JS array-related knowledge