The array technique, my love

Foreword

Arrays are one of the most common concepts in Javascript and offer us many possibilities for manipulating data.Proper array handling techniques can make our coding more efficient, so let's take a look.

1. Array deduplication

Favorite question in front-end interviews, hahaha.

"Determine whether a simple array element is repeated

function isRepeat(arr) {var hash = {};for (var i in arr) {if (hash[arr[i]]) {return true;}hash[arr[i]] = true;}return false;}

①Using ES6 Set to deduplicate
You can use it regardless of compatibility.
Note: When the content of the object is the same, because the storage address is different, it is not removed.

function unique (arr) {return Array.from(new Set(arr)); //of course there is a simpler way to write it: [...new Set(arr)]}var arr = [1,1,undefined,undefined,null,null,NaN,NaN,{},{}];console.log(unique(arr))//[1,undefined,null,NaN,{},{}]

②Using indexOf to remove duplicates
The interviewer asked me to use handwriting as my favorite method to remove duplicates from arrays. Of course, splice can also be chosen to remove duplicates.

function unique(arr) {if (!Array.isArray(arr)) {console.log('type error!');return;}var array = [];for (var i = 0; i < arr.length; i++) {if (array.indexOf(arr[i]) === -1) {array.push(arr[i]);}}return array;}

There are many methods, here are two.

2, empty array

var arr= ["a", "b", "c"];arr.length = 0;

3, merge array

①concat
is used to combine two or more arrays.This method does not change the existing array, but returns a new array.

var num1 = [1, 2, 3],num2 = [4, 5, 6],num3 = [7, 8, 9];var nums = num1.concat(num2, num3); 

②ES6 spread operator (…)

var num1 = [1, 2, 3],num2 = [4, 5, 6],num3 = [7, 8, 9];var nums = [...num1, ...num2, ...num3];

4. Conversion between strings and arrays

①String to array split
Slice the string with the specified delimiter and convert it into several array elements.

var str = '123,456,789';var strArr = str.split(',');

split application: commonly used when specifying parameters after getting the url

function GetRequest() {var url = location.search.replace(/\s+/g, ""),theRequest = {};if (url.indexOf("?") != -1) {var str = url.substr(1);strs = str.split("&");for(var i = 0; i < strs.length; i++) {theRequest[decodeURI(strs[i].split("=")[0])]=decodeURI(strs[i].split("=")[1]);}}return theRequest; //return the parameter value as an object} 

②Array to String join
Concatenate the elements of the array with the specified delimiter and convert it into a string.

var strArr = ['abc', 'def', 'hig'];var str = strArr.join(','); //When the delimiter is ',', it is consistent with the result of toString

5. Delete the array elements that meet the conditions

filter
Runs the given function on each item of the array, returning an array of items whose result is true.

var arr = ["apple", "orange","happy"];var arrRes = arr. filter(function(v){return v.length > 5;});