Several methods commonly used in arrays
push: add an item to the end of the array and the return value is the new length of
the array unshift: add an item to the beginning of the array and the return value is the new length of the array
pop: delete the end of the array and the return value is the deleted array item
shift: delete the beginning of the array item returns the first item that was deleted
splice: delete any item in the array The return value is the deleted array item
slice: copy the array The return value is the new array copied to after writing the value does not contain the last item copied
Concatenation:
concat: concatenate an array with another array to return the concatenated array
join: concatenate each item in the array into a string according to the specified delimiter
Sort:
reverse: reverse order array return value reverse order array original array change
sort: bubble sort according to anonymous function ba reverse order ab ascending order
Poor compatibility:
indexOf: returns the index of the item in the array
lastIndexOf: returns the last index of the item in the array
forEach: loops through the array parameter is an anonymous function and returns undefined by default
map: loop through the array parameter is an anonymous function
Extended use of splice: Simulate push ary.splice(ary.length,0,x) emulate pop ary.splice(ary.length-1,1) emulate unshift ary.splice(0,0,x) emulate shift ary.splice(0,1) splice(0) delete from 0 to the end ==> delete all operations ==> return all array items ==> clone the array
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The delete method of the supplementary object: (delete)
var obj = { 0: "Background", 1: "TG", 2: "AS", 3: "Crawler", 4: "User", 8: "Esports", 9: "Penguin"};
delete obj[2]console.log(obj)// {0: "Background", 1: "TG", 3: "Crawler", 4: "User", 8: "E-sports", 9: "Penguin" }
var Employee = {
age: 28,
name: 'abc',
designation: 'developer'
}
console.log(delete Employee.name); // returns true
console.log(delete Employee.age); // returns true
// 当试着删除一个不存在的属性时
// 同样会返回true
console.log(delete Employee.salary); // returns trueYou can also use delete to delete an array
var arr = [1, 2, 3, 4, 5, 6, 7, 8]
delete arr[3];
console.log(arr)//[1, 2, 3, undefined × 1, 5, 6, 7, 8]
Delete with delete, the length of the array remains unchanged, here is still 8
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Mainly explain the array interception:
The methods of array interception mainly include slice and splice. In addition, when it comes to interception, I will also bring string interception here. The main methods of string interception are substr and substring.
slice
grammar:
arrayObject.slice(start,end)
| parameter | describe |
|---|---|
| start | Required. Specifies where to start the selection. If negative, it specifies the position from the end of the array. That is, -1 refers to the last element, -2 refers to the second-to-last element, and so on. |
| end | 可选。规定从何处结束选取。该参数是数组片断结束处的数组下标。如果没有指定该参数，那么切分的数组包含从 start 到数组结束的所有元素。如果这个参数是负数，那么它规定的是从数组尾部开始算起的元素。 |
开始的下标是从0开始的，start包含，end不包含
当只有start，没有指定end时，会从开始一直截取到结束
slice（）返回的是一个新的数组
var arr=["George","John","Thomas"]
console.log(arr.slice(1)); //["John", "Thomas"]
console.log(arr); //["George", "John", "Thomas"]
②只有起始值，并且为负，默认的是从起始位置一直到整个数组结束，此处没有起始值，数组的最后一个下标是-1，比如此例，如果从-6开始取，必定是整个数组
var arr=[2,3,5,6,8,9]
var arr1=arr.slice(-1)
console.log(arr1) //[9] 只有起始参数，并且为负值，从数组尾部截取元素
④有起始值和结束值，并且为负，此处需注意下秒也是从小到大，同理，比如（-1，-6）也是肯定取不到值的，另外截取的下标个数也并不包含最后一个下标
var arr=[2,3,5,6,8,9]
var arr1=arr.slice(-6,-1)
console.log(arr1) //[2,3,5,6,8]
⑤有起始值和结束值，并且正负都有
负值到0
var arr=[2,3,5,6,8,9]
var arr1=arr.slice(-1,0)
splice
定义和用法
splice() 方法向/从数组中添加/删除项目，然后返回被删除的项目。
注释：该方法会改变原始数组。
语法
arrayObject.splice(index,howmany,item1,.....,itemX)
| 参数 | 描述 |
|---|---|
| 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。 |
因为有第三个参数，可以通过splice方法在数组的指定位置添加数据，
例如 var arr=["George","John","Thomas"]
arr.splice(1,0,'hh')
console.log(arr); ["George", "hh", "John", "Thomas"]
（3）substr 这个是字符串的用法 用法arr.substr(m,n) m必选也可以负值 n选填，注意看这个并不是结束为止而是截取的个数
示例如下：
只有一个参数 默认从此下标开始，取后面所有的
正值
var arr="sdhgfhf"
var arr1=arr.substr(1)
console.log(arr)// "sdhgfhf"这个是不变的，下面不再列举
console.log(arr1)// "dhgfhf" 从下标1开始取后面所有的
负值
var arr="sdhgfhf"
var arr1=arr.substr(-2)
console.log(arr1)// "hf" 从下标-2开始取后面所有的
两个参数，从第一个下标开始，截取到下标2的长度
var arr="sdhgfhf"
var arr1=arr.substr(1，3)
console.log(arr1)// "dhg" 从下标1开始取后面所有的 同理如果为负值，比如（-6，3）则为"hjf";后面的始终为长度
总结：此方法需注意不要和数组的混淆，这个是截取长度的
（4）substring 用法arr.substring(m,n) 两个参数，m必须，起始位置 ，n选填，截取下标的结束位置，此用法和上面slice有点类似，但是需要注意的是此方法是不支持负值的
示例如下：
只有一个参数
var arr="sdhgfhf"
var arr1=arr.substring(1)
console.log(arr1)//"dhgfhf"从下标1开始取后面所有的
两个参数
var arr="sdhgfhf"
var arr1=arr.substring(1,3)
console.log(arr1)// "dh"从下标1开始截取到下标3，但是不包含3
总结：此方法不支持负值，只针对下标来截取的
最后，以上主要是总结的数组的一些简单的操作方法，学无止境，继续努力。