Common methods of array

1. Common methods of array

  1. concat(): merge two arrays
var arr = [1,2,3,4,5,6,6];
        var arr1 = [3, 4, 5];
        var arr2 = [4, 5, 6];
        var arr3 = [8, 9, 0];
        var arr4 = ["w", "n", "q"];
        console.log(arr);
        console.log(arr1);
        console.log(arr2);
        console.log(arr3);
        console.log(arr4);
        
        var myarr = arr1.concat(arr2);
        console.log(myarr);
  1. reverse(): reverse the order of array elements
var myarr = arr.reverse();
        console.log(myarr);
        console.log(typeof myarr);
  1. join(): convert array to string, use "," link between default elements
var myarr = arr1.join();
        console.log(myarr);
        console.log(typeof myarr);
  1. tostring: converting arrays to strings
var myarr = arr.toString();
        console.log(myarr);
        console.log(typeof myarr);
  1. pop(): delete the last element of the array
arr4.pop();
console.log(arr4);
  1. push(): add one or more elements to the last face of the array
arr4.push("A","B");
console.log(arr4);
  1. unshift(): add one or more elements to the front of the array
arr4.unshift("Y");
console.log(arr4);
  1. (1) . slice(): array cutting: if arr.slice(s) There is only one parameter that represents the starting subscript value
var myarr = arr.slice(1);
        console.log(myarr);
        console.log(typeof myarr);
(2) . slice(): array cutting: if arr.slice When the (- s, - e) parameter is negative, it means to split (intercept) from the last part of the array forward - 1 means the last bit - 2 table is the second last bit
var myarr = arr.slice(-2,-1);
       console.log(myarr);
        console.log(arr);
        console.log(typeof myarr);
  1. (1) . splice(): the operation of adding, deleting and modifying an array: array name. splice(i,num);
var myarr = arr.splice(1,2);
       console.log(myarr);
       console.log(typeof myarr);
 (2). splice():  arr.splice(i,num,"item","item"); when there are more than two parameters: operate the original array i: represent subscript num: represent number item: represent new element (new original array) will change the original array; return value is a new array: the element of the new array is composed of the element cut from the original array
var myArr = arr.splice(1,2,777,999);
        console.log(myArr);
        console.log(arr);
  1. indexof(): check if an element exists in the array arr.indexOf(item);
var myArr = arr.indexOf(6);
          console.log(myArr);
var myArr = arr.lastIndexOf(6);
          console.log(myArr);

Iterative method of array, higher order function

  1. forEach(): a collection used to traverse arrays of array classes
let arr = [1,3,'Zhang San','hello'];

    arr.forEach((item,index) => {
        console.log(index + ":" + item);
    });

    let cheks = document.querySelectorAll("input");
    cheks.forEach(currentItem => {
        console.log(currentItem);
    });
    console.log([...cheks]);
    var result = [...cheks].every( item => {
        return item.checked;
    });
    console.log(result);
  1. map(): returns a new array of qualified elements
let arr2 = [1,2,3,4,5];

    // let arr3 = arr2.map(function(item){
    //     return item + 1;
    // });

    // let arr3 = arr2.map((item) => {
    //     return item + 1;
    // });

    let arr3 = arr2.map(item => item + 1);
    console.log(arr3);
  1. Filter(): returns an array of elements whose condition is true
let arr4 = [1,2,3,4,5];
    let arr5 = arr4.filter((item) => {
        return item > 3;
    });
    console.log(arr5);
  1. some(): returns true if one of the conditions is true
let arr6 = [11,2,51,4,45];
    let result2 = arr6.some((item) => {
        return item > 50;
    });
    console.log(result2);
  1. every(): all elements return true if the condition is true, one of them is false or false)
let arr7 = [11,2,51,4,45,0];
    let result3 = arr7.every(item => item > 0);
    console.log(result3);
  1. reduce(): achieve cumulative effect
let sum = arr8.reduce( (now,total) => {
        console.log(now,total);
        return now + total;
    });
    console.log(sum);

Posted on Mon, 22 Jun 2020 23:53:24 -0400 by whiteboikyle