JavaScript Array Manipulation methods

Defining arrays

var arr = [];

var arr = new Array ();

var arr = new Array (10); Create an array of length 10

Array manipulation methods

1. join (): tells the array that all elements are converted to strings and concatenated together, you can specify an optional string to separate the elements of the array, and do not change the original array

   var arr = [n/a];

Console.log (Arr.join ("-")); The

Console.log (typeof Arr.join ("-")); String

Console.log (arr); [A]

2. Reserve (): Reverses the order of the elements in the array, returns an array of reverse orders, and changes the original array

var arr = [n/a];

Console.log (Arr.reverse ()); [3,2,1]

3. Sort (): Sorts the elements in the array and returns the sorted array, changing the original array (numbers are from small to large according to the first number, letters are capitalized in alphabetical order before lowercase, undefined at the tail)

var a = [1,3,2];

Console.log (A.sort ()); [A]

Console.log (a); [A]

var arr = ["A", "D", "C"];

Console.log (Arr.sort ()); ["A", "C", "D"]

var arr = [ -3,0,1];

Console.log (Arr.sort ()); [ -3,0,1]

Sort () sorts a number negative 0 positive

Sort () calls the ToString () method when sorting, and then compares it against the ASCII code

Use sort () to sort the numbers in ascending order

var arr = [0,2,1,0.5];

Console.log (Arr.sort (A, b) {

return a-B;

));

Use sort () to sort numbers in descending order

var arr = [0,2,1,0.5];

Console.log (Arr.sort (A, b) {

return b-a;

}));

4. concat () creates and returns a new array without changing the original array

var arr = [n/a];

Console.log (Arr.concat ([up])); [1,2,3,1,2]

Console.log (arr); [A]

5. Slice () returns the specified Subarray, the starting position of the two arguments, the end position, and the default from the beginning to the end of the argument.

do not change the original array

var arr = [1,2,3,4,5];

Console.log (Arr.slice (1,3)); [2,3]

Console.log (arr); [1,2,3,4,5]

6. Splice () method of inserting or deleting elements in an array, changing the original array , the first parameter is the starting position, the second is the number of deleted elements, and the subsequent argument is the inserted element

var arr = [1,2,3,4,5];

Console.log (Arr.splice (2,1));//[3]

Console.log (arr); [1,2,4,5]

Console.log (Arr.splice (2,0,3)); //[]

Console.log (arr); [1,2,3,4,5]

7. push () adds one or more elements at the end of the array, changing the new length of the new array, the original array

pop () removes the last element of the array, changing the last element deleted by the original array .

var arr = [1,2,3,4,5];

Console.log (Arr.push (1));

Console.log (arr);

Console.log (Arr.pop ()); Returns the deleted element

Console.log (Arr.pop ());

8. unshift () add one or more elements at the header of the array, changing the new length of the array, the original array

shift () removes the first element of the array, changing the first element, deleted by the original array

var arr = [1,2,3,4,5];

Console.log (arr.unshift (0)); Returns the new length of the array

Console.log (Arr.shift ()); 0, returns the first element deleted

ECMA5 newly added array operation methods

9. ForEach () iterates through the array, unable to terminate the traversal before all elements are passed to the calling function, with three parameters, an array element, an element index, and a

var data = [1,2,3,4];

Data.foreach (function (v,i,a) {

Console.log (A[i] = v + i); [1,3,5,7];

});

map () calls each element of the array to the specified function and returns an array

var arr = [n/a];

var data = Arr.map (function (x) {return x*x});

Console.log (data); [1,4,9]

The array element returned by filter () is a subset of the call array, and the passed function is used for logical judgment.

var arr = [n/a];

var data = Arr.filter (function (x) {return x < 3;});

Console.log (data); [Up]

every () Some () the array element is applied to the specified function to determine, return TRUE or False

Every () equals, false, which can stop traversing

Some () equals or, if true, can stop traversing

var arr = [1,2,3,4,5];

Console.log (Arr.every (function (x) {

Console.log (x); Output 1, false, stop traversal

return x%2 = = 0;

}));

Console.log (Arr.some (function (x) {

Console.log (x); True when output 1 2,2, stop traversal

return x%2 = = 0;

}));

reduce () reduceright () combines array elements using the specified function, generating a single value, two arguments, first an action function, and a second as the initial value

Reduce () from low index to high index;

Reduceright () from high index to low index;

var arr = [1,2,3,4,5];

Console.log (Arr.reduce (function (x, y) {

Console.log (x);

Console.log (y);

return x + y;

},0)); 15

Console.log (Arr.reduceright (function (x, y) {

Console.log (x);

Console.log (y);

return x + y;

},0)); 15

indexOf () lastIndexOf (), returns the index of the first element searched, without searching to return-1;

var arr = [1,2,3,4,5,1];

Console.log (Arr.indexof (1)); 0

Console.log (Arr.lastindexof (1)); 5

Console.log (Arr.indexof (10)); -1

15. Three ways to detect arrays

Typeof,instanceof,isarray (newly added in E5)

Typeof:typeof arr If an array returns an object

Instanceof:arr instanceof Array returns true for arrays

IsArray:Array.isArray (arr); If the array returns true

var arr = [1,2,3,4,5];

Console.log (typeof arr); Object

Console.log (arr instanceof Array); True

Console.log (Array.isarray (arr)); True

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JavaScript Array Manipulation methods