Explanation of JavaScript related functions

There are some functions that frequently appear in JavaScript learning. This article will explain some of them in detail.

.map

The map method will iterate through each element in the array, process each element according to the callback function, and finally return a new array.

Use the map method to add 3 to each item in oldArray and save them in newArray. oldArray should not be changed.

var oldArray = [1,2,3,4,5];var newArray = oldArray.map(function(val){  return val + 3;  });
.reduce

The elements in the array are operated on in sequence from left to right, and the last remaining element is the return value
The cumulative value of the last result (previousVal) and the current value (currentVal).

var array = [4,5,6,7,8];var singleVal = 0;singleVal = array.reduce(function(previousVal, currentVal){ return previousVal + currentVal;   });
.filter

The filter method is used to iterate an array and filter out matching elements according to the given conditions.

Use filter to create a new array. The value of the new array is the elements in oldArray whose value is less than 6. The original array is not allowed to be changed. oldArray

var oldArray = [1,2,3,4,5,6,7,8,9,10];var newArray = oldArray.filter(function(val){    return val<6;   });
.sort

sort method will change the original array and return the sorted array. sort can pass comparison functions as arguments. The comparison function has a return value. When a is less than b, it returns a negative number; when a is greater than b, it returns a positive number; when they are equal, it returns 0. If no comparison function is passed in, it will convert all values ​​into strings and sort them alphabetically.

Use sort to sort the array from small to large.

var array = [1, 12, 21, 2];array.sort(function(a, b) {  return a - b;});result: [1,2,12,21]
.reverse

Use reverse to flip the array array. And assigned to newArray.

var array = [1,2,3,4,5,6,7];var newArray = [];newArray = array.reverse();
reverse_result.png
.concat

concat The parameter of the method should be an array. The array in the parameter will be concatenated after the original array and returned as a new array.

Use .concat() to splice concatMe behind oldArray and assign it to newArray.

concat_result.png
.split

You can use the split method to split a string into an array by a specified delimiter. Pass a parameter to the split method, which will be used as a separator.

Use the split method to split the string string into an array array.

No delimiter.

<script type="text/javascript">
    var str="How are you doing today?";    var n=str.split();    document.write(n);</script>输出：
How are you doing today?

Separate each character of the string.