This article brings you an introduction to common array operations in JavaScript (code examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
In daily development, the front-end processing of data is inseparable. Here we will sort out the new array api of ES6/ES7/ES8...
Flat n-dimensional array
Array.flat() -- ES10
The method will recursively traverse the array according to a specifiable depth and traverse all elements to The elements in the subarrays are combined into a new array and returned. Array.flat(n) is the API for flat arrays. n represents the dimension. When the n value is Infinity, the dimension is infinite.
[1,[2,3]].flat(2) //[1,2,3] [1,[2,3,[4,5]].flat(3) //[1,2,3,4,5] [1,[2,3,[4,5]]].toString() //'1,2,3,4,5' [1,[2,3,[4,5],[...]]].flat(Infinity)
The flat() method will remove empty items in the array:
var arr4 = [1, 2, , 4, 5]; arr4.flat(); // [1, 2, 4, 5]
Alternative solution: The essence is to use recursion and the array merging method concat to achieve flatness
function flatten(arr) {
while(arr.some(item=>Array.isArray(item))) {
arr = [].concat(...arr);
}
return arr;
}
flatten([1,[2,3]]) //[1,2,3]
flatten([1,[2,3,[4,5]]) //[1,2,3,4,5]From and set are used to deduplicate arrays; set is a new data type in ES6 that defines non-repeating arrays. Array.from converts a class array into an array.
Array.from(new Set([1,2,3,3,4,4])) //[1,2,3,4] [...new Set([1,2,3,3,4,4])] //[1,2,3,4]
Alternative solution:
Array.prototype.distinct = function(){
var arr = this,
result = [],
i,
j,
len = arr.length;
for(i = 0; i < len; i++){
for(j = i + 1; j < len; j++){
if(arr[i] === arr[j]){
j = ++i;
}
}
result.push(arr[i]);
}
return result;
}
[1,2,3,3,4,4].distinct(); //[1,2,3,4]Array de-coupling and merging
function combine(){
let arr = [].concat.apply([], arguments); //没有去重复的新数组
return Array.from(new Set(arr));
}
var m = [1, 2, 2], n = [2,3,3];
console.log(combine(m,n));[1,2,3,4].sort((a, b) => a - b); // [1, 2,3,4],默认是升序 [1,2,3,4].sort((a, b) => b - a); // [4,3,2,1] 降序
Alternative solution: ascending order
Array.prototype.bubleSort=function () {
let arr=this,
len = arr.length;
for (let outer = len; outer >= 2; outer--) {
for (let inner = 0; inner <= outer - 1; inner++) {
if (arr[inner] > arr[inner + 1]) {
//升序
[arr[inner], arr[inner + 1]] = [arr[inner + 1], arr[inner]];
//console.log([arr[inner], arr[inner + 1]]);
}
}
}
return arr;
}
[1,2,3,4].bubleSort(); //[1,2,3,4]Return the maximum value in a given set of numbers. If at least one of the given arguments cannot be converted to a number, NaN is returned.
Math.max(...[1,2,3,4]) //4
Math.max.apply(this,[1,2,3,4]) //4
[1,2,3,4].reduce( (prev, cur,curIndex,arr)=> {
return Math.max(prev,cur);
},0) //4Math.max() is a built-in method of the Math object, and the parameter is a string;
reduce is the ES5 array api, and the parameters include functions and default initial values;
The function has four parameters , pre (last return value), cur (current value), curIndex (current value index), arr (current array)
[1,2,3,4].reduce(function (prev, cur) {
return prev + cur;
},0)Replacement scheme: sum, Use slice to intercept and change the array, and then use recursive summation
function sum(arr) {
var len = arr.length;
if(len == 0){
return 0;
} else if (len == 1){
return arr[0];
} else {
return arr[0] + sum(arr.slice(1));
}
}
sum([1,2,3,4]);The concat() method is used to merge two or more arrays. This method does not change the existing array, but returns a new array.
push() method adds one or more elements to the end of an array and returns the new length of the array.
[1,2,3,4].concat([5,6]) //[1,2,3,4,5,6]
[...[1,2,3,4],...[4,5]] //[1,2,3,4,5,6]
// 相当于 vegetables.push('celery', 'beetroot');
Array.prototype.push.apply( ['parsnip', 'potato'], ['celery', 'beetroot']);
console.log(vegetables);Replacement plan:
let arr=[1,2,3,4];
[5,6].map(item=>{
arr.push(item)
}) //arr值为[1,2,3,4,5,6]includes(), find(), findIndex() are ES6 api
[1,2,3].includes(4)//false [1,2,3].indexOf(4) //-1 如果存在换回索引 [1, 2, 3].find((item)=>item===3) //3 如果数组中无值返回undefined [1, 2, 3].findIndex((item)=>item===3) //2 如果数组中无值返回-1
Replacement Solution:
[1,2,3].some(item=>{
return item===3
}) //true 如果不包含返回falseClass array: has a length attribute, but the attribute is a non-negative integer. It doesn't have some methods of arrays, but that doesn't mean it can't use array methods.
For example: the value returned by document.getElementsByTagName('p') is an array class
call, apply: changes this in the slice to point to arguments, so arguments can also call the array method
Array.from is Create an array-like or iterable object as an array
The slice() method in the array object cuts the array without operating the original array, which can be called a shallow copy
var a={
0:"aa",
1:"cc",
2:"dd",
length:3
}
var callArr = Array.prototype.slice.call(a);
var applyArr = Array.prototype.slice.apply(a)
var fromArr = Array.from(a)
console.log(a,callArr, applyArr, fromArr);Array.prototype.slice Understanding:
Array.prototype.slice = function(start,end){
var result = new Array();
start = start || 0;
end = end || this.length; //this指向调用的对象，当用了call后，能够改变this的指向，也就是指向传进来的对象，这是关键
for(var i = start; i < end; i++){
result.push(this[i]);
}
return result;
}[1,2,3].fill(1) [1,2,3].map(()=>0)
[1,2,3].every(item=>{return item>2})// false [1,2,3].some (item=>{return item>2})// truemethod creates a new array containing all elements of the test implemented by the provided function.
[1,2,3].filter(item=>{return item >=2 });fromEntries
Object.keys({name:'张三',age:14}) //['name','age']
Object.values({name:'张三',age:14}) //['张三',14]
Object.entries({name:'张三',age:14}) //[[name,'张三'],[age,14]]
Object.fromEntries([name,'张三'],[age,14]) //ES10的api,Chrome不支持 , firebox输出{name:'张三',age:14}new Map() constructor accepts an iterable entry. With the help of the Object.entries method, you can easily convert Object to Map:
var obj = { foo: "bar", baz: 42 };
var map = new Map(Object.entries(obj));
console.log(map); // Map { foo: "bar", baz: 42 }[Related recommendations: JavaScript Video Tutorial]
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