JavaScript array detail (JS array depth parsing)

The Array object is a composite type used to store multiple values in a single variable, each of which can be of different value types.

Ways to create an array object:

New Array (); New Array (size); New Array (element0, Element1, ..., ELEMENTN);

1.  when the index value is negative, it is treated as a property of the object, and if it is a non-negative numeric string, it is implicitly converted to a numeric index:

      var New Array ();      a[-1.23]=true;      a[1]= "pomelo";      a["]=" "tt";      Console.log (a);    // /  [1: "Pomelo", +: "tt", -1.23:true]      Console.log (a.length)   ///101 The length of the  sparse array is the maximum subscript +1

In fact, the index of the array object is actually a special form of the object property name, when trying to query any object property name, will not error, but will display undefined:

Console.log (a["Hello"]);   // undefined

2. The Length property can be used to place an empty array or to intercept an array from the front:

    var array1=[1,2,3,4,5];    Array1.length=3;   // /[1,2,3]    array1.length=0;   // /[]    array1.length=5;   // /[] Empty array    of length 5 Console.log (array1)

You can use the Object.defineproperty (object, property name, {settings}) method to set the readable writable:

    Object.defineproperty (array1, "Length", {writable:false});    Array1.length=10;    Console.log (array1.length);     // /5

3. Adding and removing array elements:

End: add element push (), delete element pop ();

Header: add element unshift (), delete element shift ();

    var array2=[1,2,3,4,5];    Array2.unshift (6);   // /[6,1,2,3,4,5]    Array2.shift ();   // [1,2,3,4,5]    Console.log (array2);

4. Convenient optimization and selection of arrays

When the size of the array is large, length should not be queried in each loop;

When you need to filter invalid data in the array, use continue to jump out of the loop;

var array3=[null,1,0,undefined];
for (var i= 0,len=array3.length;i<len;i++) {
    if (!array3[i]) continue;
    Console.log (Array3[i]);   1
}

or use the foreach () method that comes with ES5:

    var array4=[1,2,3,4];     var sum=0;    Array4.foreach (function(i) {        sum+ =i;    });    Console.log (sum);    // /10

5.js does not support multidimensional arrays, but can be implemented by arrays of arrays:

    var array5=New Array (ten);      for (var i=0;i<array5.length;i++) {        array5[i]=new Array (ten);    }      for (var i=0;i<array5.length;i++) {        for (var j=0;j<array5[i]. length;j++) {            array5[i][j]=i*j;        }    }    Console.log (array5[5][6]);   //  -

6. Array methods

6.1 Join () converts an array into a string and joins together

    var array6=[1,2,3];    Console.log (Array6.join ("-"));  // 1*2*3    Console.log (Array6.join (""));  // 123    Console.log (Array6.join ());  //  the    Console.log (typeof Array6.join ());  // String

6.2 Reverse () reverses the order of elements based on the original array itself

var array7=[1,2,3];
Console.log (Array7.reverse ())  //[3,2,1]

6.3 sort () array sorting

      var array8=["Apple", "Cherry", "cherry"];      Console.log (Array8.sort ());     // ["Apple", "Cherry", "cherry"]       array8.push (undefined);      Console.log (Array8.sort ());    // undefined will be put to the end ["Apple", "Cherry", "cherry", undefined]

If you want to change the collation, you need to pass in a comparison function:

    var array9=[33,4,11,222];                                                     Console.log (Array9.sort ());    // 11,222,33,4   Default compares                  Console.log with the first number    (Array9.sort (A, b) {             //  arrange               return from small to large (         b;                                                               })                                                                                                                                               )

Character sorting is small in size by default, with the first letter ASCII encoded as the basis, from small arrivals to sort:

    vararray10=["Ant", "Boy", "Cat", "Dog"];      Console.log (Array10.sort ()); //["Boy", "Dog", "Ant", "cat")Console.log (Array10.sort (function(s,t) {varA=s.tolowercase (); varb=t.tolowercase (); if(A<B)return-1; if(A>B)return1; return0;         })                                                                   ); //["Ant", "Boy", "Cat", "Dog")

6.4 concat () array connection

     var array11=[1,2,3];                                                                    Console.log (Array11.concat (4,5));     // [1,2,3,4,5]                                      Console.log (Array11.concat ([4,5]));    // [1,2,3,4,5]                                     Console.log (Array11.concat ("4", [5,[6,[7,8]]))       //[1, 2, 3, "4", 5, array[2]]   

6.5 Slice (first position, second position)

Returns a sub-array from the first position (including) to the second position;

Returns a subarray of all elements from the specified position to the end of the array, if only one argument is drawn;

If the parameter has a negative number, it identifies the subscript from the position of the back-forward;

    var array12=[1,2,3,4,5];                              Console.log (Array12.slice (0,3));   // [A]          Console.log (Array12.slice (3));    // [4,5]             Console.log (Array12.slice ( -1));   // [5]               Console.log (Array12.slice (1,-1));   // [2,3,4]     

6.6 Splice (The starting position of the insertion or deletion, the number of elements removed) a common way to insert, delete, or replace elements in an array:

    vararray13=[1,2,3,4,5,6,7,8]; //DeleteConsole.log (Array13.splice (4));//[5,6,7,8]Console.log (ARRAY13);//[1,2,3,4]Console.log (Array13.splice);//[2,3]Console.log (ARRAY13);//[1,4]    //InsertArray13.splice (1,0, "pomelo");      Console.log (ARRAY13); //[1, "Pomelo", 4]    //Replace    vararray14=[1,2,3,4,5]; Array14.splice (2,1, "pomelo");//[1, 2, "Pomelo", 4, 5]Console.log (ARRAY14)

6.7 map () passes each element of the array that calls this function to the specified function:

    var array15=[1,2,3];                               var array16=array15.map (function(i) {                  return i*i;                                   });                                               Console.log (ARRAY16)    //[1,4,9]             

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JavaScript array detail (JS array depth parsing)