Of Stack

Daily javascript Summary (Array array)

  • 2020-10-31 21:36:42
  • OfStack

1. Common methods of arrays 


var colors = ["red", "blue", "green"];  //creates an array with three strings
    alert(colors.toString());  //red,blue,green
    alert(colors.valueOf());   //red,blue,green
    alert(colors);        //red,blue,green

2, the array map() method 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]

3, array reduce() method 


 var values = [1,2,3,4,5];
     // receive 1 I'm going to go from left to right item Until the reduce to 1 A value. 
    var sum = values.reduce(function(prev, cur, index, array){
      console.log(array === values);
      console.log(index);//1,2,3,4  Array index from 1 start 
      return prev + cur;// Add the two values before and after 
    });
    alert(sum);//15

4, array concat() method 


//concat()  Method is used to join two or more arrays. 
    // This method does not change the existing array, but only returns the connected array 1 A copy. 
    // grammar 
    //arrayObject.concat(arrayX,arrayX,......,arrayX)
    var colors = ["red", "green", "blue"];
    var colors2 = colors.concat("yellow", ["black", "brown"]);
    
    alert(colors);   //red,green,blue    
    alert(colors2);  //red,green,blue,yellow,black,brown

5. Array length length 


 var colors = new Array(3);   //create an array with three items
    var names = new Array("Greg"); //create an array with one item, the string "Greg"

    alert(colors.length);//3
    alert(names.length);//1



 var colors = ["red", "blue", "green"]; //creates an array with three strings
    var names = [];            //creates an empty array
    var values = [1,2,];          //AVOID! Creates an array with 2 or 3 items
    var options = [,,,,,];         //AVOID! creates an array with 5 or 6 items
    
    alert(colors.length);  //3
    alert(names.length);   //0
    alert(values.length);  //2 (FF, Safari, Opera) or 3 (IE)
    alert(options.length);  //5 (FF, Safari, Opera) or 6 (IE)



var colors = ["red", "blue", "green"];  //creates an array with three strings
    colors.length = 2;
    alert(colors[2]);    //undefined


var colors = ["red", "blue", "green"];  //creates an array with three strings
    colors.length = 4;
    alert(colors[3]);    //undefined



 var colors = ["red", "blue", "green"];  //creates an array with three strings
    colors[colors.length] = "black";     //add a color
    colors[colors.length] = "brown";     //add another color

    alert(colors.length);  //5
    alert(colors[3]);    //black
    alert(colors[4]);    //brown



var colors = ["red", "blue", "green"];  //creates an array with three strings
    colors[99] = "black";           //add a color (position 99)
    alert(colors.length); //100

6. Array methods every and some 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
0

7, array filter() method 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
1

8. Arrays indexOf and lastIndexOf 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
2

9. Arrays toLocaleString and toString 


 var person1 = {
      toLocaleString : function () {
        return "Nikolaos";
      },
      
      toString : function() {
        return "Nicholas";
      }
    };
    
    var person2 = {
      toLocaleString : function () {
        return "Grigorios";
      },
      
      toString : function() {
        return "Greg";
      }
    };
    
    var people = [person1, person2];
    alert(people);           //Nicholas,Greg
    alert(people.toString());      //Nicholas,Greg
    alert(people.toLocaleString());   //Nikolaos,Grigorios

10. Array push and pop methods 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
4

11. Array methods unshift and shift 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
5

12. Reverse array reverse 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
6

13, array sorting method sort 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
7

14. Array method slice 


/*
      slice()  Method returns the selected element from an existing array. 
       grammar 
      arrayObject.slice(start,end)
      start   A necessity. Specify where to start. If it is negative, it specifies the position from the end of the array. In other words, -1  Refers to the final 1 An element, -2  Refers to the bottom first 2 Elements, and so on. 
      end     Optional. Specify where to end the selection. This parameter is the array index at the end of the array fragment. If this parameter is not specified, the sharded array contains the  start  All elements to the end of the array. If the argument is negative, it specifies the element that is counted from the end of the array. 
       The return value 
       return 1 A new array containing an array from  start  to  end  Not including the element  arrayObject  Element. 
    */
    var colors = ["red", "green", "blue", "yellow", "purple"];
    var colors2 = colors.slice(1);
    var colors3 = colors.slice(1,4);
    
    alert(colors2);  //green,blue,yellow,purple
    alert(colors3);  //green,blue,yellow

15. Array method splice 


var numbers = [1,2,3,4,5,4,3,2,1];
    
    var mapResult = numbers.map(function(item, index, array){
      //item  Array element  index Element corresponding index  array The original array 
      console.log(array === numbers);//true
      return item * 2;
    });
    console.log(mapResult);  //[2,4,6,8,10,8,6,4,2]
9

16, array isArray() method 


alert(Array.isArray([]));  //true
    alert(Array.isArray({}));  //false

The above is the summary of today's javascript study, and I will continue to update it every day. I hope you will continue to pay attention.

Related articles: