JavaScript arrays and mathematical objects

Creating an array:

       var ary1 = new new the Array (); 
       the console.log (ary1); // [] 


       var ary2 = new new the Array ( 2 , . 3 , . 4 , . 5 ); 
       the console.log (ary2);   // [2,3,4, . 5] 

       var ary3 = new new the array ( . 4 ); // pass a parameter for the number representing the length of the array 
       the console.log (ary3);   // [* empty. 4] 
       
       ary3.length = . 8 ; // length attribute array may be reading can write 
       console.log (ary3);   // [empty * 8]

An array of methods:

push（）

• Features: Add item to the end of the array;
• Parameters: add items into the array, one or more of;
• Return value: new length number;
• Change the original array

pop（）

• Function: Remove one at the end of the array;
• Parameters: no;
• Returns: delete the item;
• Change the original array

unshift（）

• Function: Adds an item at the beginning of the array;
• Parameters: add items into the array, one or more of;
• Return value: new length number;
• Change the original array

shift（）

• Function: Remove one at the beginning of the array;
• Parameters: no;
• Returns: delete the item;
• Change the original array

splice（）

• Function: Extract the specified item in the array;
• parameter:

          (n) taken from the index n to the start end of the array 
          (n, m), taken from the start index n m pieces of 
          parameters after the (n, m, x, y , z) m as an array from the array entry added to the extraction position

• Return Value: intercepting a new array of items;
• Change the original array

slice（）

• Function: Copy items from the array;
• parameter:
  (N) from the copy start to the end of the array index n

  (N, m) from the start copying index n to the index m (not including m)
• Returns: an array of items copied out of the composition;
• Does not change the original array

join（）

• Function: the specified array connector, to string;
• Parameters: connector, the default is a comma;
• Return value: String;
• Does not change the original array

    var str1 = ary.join('<span>'+val+'</span>');
    p.innerHTML = str1;

   

concat（）

• Function: the key array or arrays assembled into an array;
• Parameters: single or array;
• Return Value: spliced ​​array;
• Does not change the original array

indexOf（）

• Function: Find an index in the array of values;
• Parameters: The item to find;
• Return Value: Index;
• Does not change the original array

reveres（）

• Function: Descending array;
• Parameters: no;
• Return Value: reverse after the original array;
• Change the original array

sort（）

• Features: Sorting an array;
• Parameters: parameter does not pass, the default characters arranged in ascending order of encoding;

              Row of numbers: 
              function (A, B) { return A- B}; ascending 
              function (A, B) { return B- A}; descending 
              row letters: 
              function (A, B) { return a.localeCompare (B)} ; ascending 
              function (a, b) { return b.localeCompare (A)}; descending 
              row Chinese: 
              function (a, b) { return a.localeCompare (B, ' ZH ' )}; ascending 
              function (a, b) { return b.localeCompare (a, ' ZH ' )}; in descending order 
              according to each of an array of a sort attribute 
              function (a, b) {return a.name.localeCompare(b.name,'zh')};
              function(a,b){ return a.age-b.age};

• Return Value: original sorted array;
• Change the original array

Iterative method array:

        Array-based methods can not be used directly supplied array, the array need to be converted to an array type in order to use

 ```
            var  ary = [3,7,4,9];
            var res = ary.every(function(item,index){
                return item > 2;
            });
            console.log(res);  //true


            var res = ary.some(function(item,index){
                return item > 5 ;
            })
            console.log(res); //true


            var res = ary.filter(function(item,index){
                return item%2 == . 1 ; 
            }) 
            the console.log (RES);   // [3,7,9] 

            // forEach array traversal is simply to look 
            var RES = ary.forEach (function (Item, index) { 
                the console.log ( index + ' : ' + Item); 
            }) 
            the console.log (RES);   // undefined 

            var RES = ary.map (function (Item, index) {
                 return Item + . 1 ; 
            }) 
            the console.log (RES); // [4, 8, 5, 10] 

 `` `    

 

Mathematical objects:

• Math.abs () - absolute value;
• Math.ceil () - rounding up;
• Math.floor () - rounded down;
• Math.min () - a minimum value;
• Math.max () - maximum value;
• Math.pow (n, m) - n m-th power;
• Math.sqrt (m) - the square root of m;
• Math.random () - Get 0-1 randomly float;
• Obtaining a random number between nm

              function getRandom(n,m){
                  return parseInt(Math.random()*(m-n+1)+n);
              }