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Array functions and precautions in jsMar 13, 2018 pm 04:47 PM
javascriptfunctionPrecautions

This article mainly shares with you the array functions and precautions in js. First, let's share with you what array objects are in js. I hope it can help you.

What are the array objects of js

  1. push — Add one or more elements to the end of the array and return the new length.

  2. pop — Delete and return the last element of the array

  3. shift — Delete and return the first element of the array

  4. unshift —Adds one or more elements to the beginning of the array and returns the new length.

  5. slice — Return selected elements from an existing array

  6. sort — Sort the elements of the array

  7. join —Put all elements of the array into a string. Elements are separated by the specified delimiter.

  8. concat — Concatenates two or more arrays and returns the result.

  9. reverse —Reverse the order of elements in an array.

  10. splice — Removes elements and adds new elements to an array.

Usage Notes

  1. push and unshift both return the new length

  2. pop , shift deletion returns the deleted value

    var Arr1 = ['11','22','33']
    var a = Arr1.push('44');
    console.log(a);  //4
    console.log(Arr1);//["11", "22", "33", "44"]
    
    var c = Arr1.pop();
    console.log(c); //44
    console.log(Arr1);//["11", "22", "33"]
    
    var d = Arr1.pop();
    console.log(d);//33
    console.log(Arr1);//["11", "22"]
    
    var Arr2 =['a','b','c']
    var b =Arr2.unshift('-a');
    console.log(b); //4 
    console.log(Arr2); // ["-a", "a", "b", "c"]
    
    
    var e = Arr2.shift();
    console.log(e); //-a
    console.log(Arr2); // ["a", "b", "c"]
    
    var f = Arr2.shift();
    console.log(f); //a 
    console.log(Arr2); // ["b", "c"]
  3. slice and splice
    slice returns a new array that has nothing to do with the original array and will not affect the source object
    parameters (start , end) where to start (if it is a negative number, count from the end), and where to end (if it is a negative number, count from the end)

    var Arr1 = ['11','22','33']
    var a = Arr1.slice(0);
    console.log(a);
    Arr1[0] = '111';
    console.log(a);
    console.log(Arr1);

    splice will split the source object

    arrayObject.splice(index,howmany,item1,.....,itemX)
    
    index   必需。整数,规定添加/删除项目的位置,使用负数可从数组结尾处规定位置。
    howmany 必需。要删除的项目数量。如果设置为 0,则不会删除项目。
    item1, ..., itemX   可选。向数组添加的新项目
    
    var Arr1 = ['11','22','33','44','55'];
    var a = Arr1.splice(1,5);
    console.log(a); // ["22", "33", "44", "55"]
    console.log(Arr1); //["11"]
    
    
    var Arr1 = ['11','22','33','44','55'];
    var a = Arr1.splice(1,5,'66','77','88');
    console.log(a);["22", "33", "44", "55"]
    console.log(Arr1); ["11", "66", "77", "88"]
  4. sort

    arrayObject.sort(sortby)
    sortby  可选。规定排序顺序。必须是函数。
    
    function sortNumber(a,b)
    {
    return -(a - b)
    }
    
    var arr = new Array(6)
    arr[0] = "10"
    arr[1] = "5"
    arr[2] = "40"
    arr[3] = "25"
    arr[4] = "1000"
    arr[5] = "1"
    console.log(arr.sort(sortNumber))//["1000", "40", "25", "10", "5", "1"]
  5. Conversion of strings and arrays

    var arr = new Array(6)
    arr[0] = "10"
    arr[1] = "5"
    arr[2] = "40"
    arr[3] = "25"
    arr[4] = "1000"
    arr[5] = "1"
    var a = arr.join('-');
    console.log(a);//10-5-40-25-1000-1
    var b = a.split('-');
    console.log(b);//["10", "5", "40", "25", "1000", "1"]
  6. concat
    will generate a new array, not Affects the original array

Related recommendations:

The most practical JS array function organization

Commonly used array functions What are the explanations of

JavaScript native array functions

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