1.map() method

• Calling a method for each element in the array does not change the original array
• exp:
```   var arr = [ '10','20','30','40','50' ]
var num1 = arr.map( ( el,index )=>{
el = el*2
// arr or ['10 ',' 20 ',' 30 ',' 40 ',' 50 ']
} )
```

2.forEach()

• Calling a method for each element in the array will change the original array
• exp:
```   var arr = [ '10','20','30','40','50' ]
var num1 = arr.forEach( ( el,index )=>{
el = el*2
// At this time, arr changes to ['20 ',' 40 ',' 60 ',' 80 ',' 100 ']
} )
```

3.filter()

• Match each item in the array, return the item that meets the condition as a new array, without changing the original array
```    var arr = [10,20,30,40,50]
var num1 = arr.filter( ( item,index )=>{
return item > 30
} )
// Now num1 is [40,50]
```

4.every()

• Judge all elements in the array and return a Boolean value. If all elements are satisfied, return true. Otherwise, return false
```    var arr = [10,20,30,40,50]
var num1 = arr.every( ( item,index )=>{
return item > 30
} )
// Now num1 is false, because not all the numbers are smaller than 30
```

5.some()

• Judge the elements in the array. If one element in the array meets the conditions, it returns true. Otherwise, it returns false
```    var arr = [10,20,30,40,50]
var num1 = arr.some( ( item,index )=>{
return item > 40
} )
// Now num1 is true because there are elements larger than 40
```

6.reduce()

*Call the function on all elements in the array, and the return value is the final result

```    var arr = [10,20,30,40,50]
var num1 = arr.reduce( ( item,index )=>{
return item + index
} )
//  At this time, num1 is 150, because each item in the array is stacked
```

7.push()

• Add an array after the last item of the array,
• Will change the original array
• The return value is the length of the new array
```    var arr = [10,20,30,40,50]
var num1 = arr.push( 60 )
// num1 = 6，
```

8.pop()

• Delete last entry of array
• Will change the original array
• The item whose return value is deleted
```    var arr = [10,20,30,40,50]
var num1 = arr.pop()
// num1 = 50 the item whose return value is deleted
```

9.shift()

• Delete first entry of array
• Will change the original array
• The item whose return value is deleted
```    var arr = [10,20,30,40,50]
var num1 = arr.shift()
// num1 = 10 the item whose return value is deleted
```

10.unshift()

• Add one or more arrays before the first item of the array
• Will change the original array
• The return value is the length of the new array
```    var arr = [10,20,30,40,50]
var num1 = arr.unshift( 60 )
// num1 = 6
```

11.isArray()

• Determine whether an object is an array
• The return value is a Boolean value
```    var arr = [10,20,30,40,50]
var num1 = Array.isArray( arr )
// num1 = true
```

12.concat()

• Splicing two arrays
• The original array will not be changed
• The return value is a new array
```    var arr = [10,20,30,40,50]
var str = [70,80]
var num1 = arr.concat( str )
// Now num1 = [10,20,30,40,50,70,80]
// Simple splicing method of es6 array:
[...arr,...str]
```

13.toString()

• The array can be converted into a string to realize splicing
• The original array will not be changed
• The return value is a string converted from an array
```    var arr = [10,20,30,40,50]
var num1 = arr.toString(  )
```

14.join()

• Convert array to string, simple conversion
• The original array will not be changed
• The return value is a string converted from an array
```    var arr = [10,20,30,40,50]
var num1 = arr.join(  )
```

15.splice()

• Add, delete and modify arrays
• The original array will be modified
• The return value is the modified item
```    var arr = [10,20,30,40,50]
var num1 = arr.splice( 0,1,60 )
// Now num1 = [10], arr = [60,20,30,40,50]
```

16 Array.from(arrayLike,mapFn,thisArg)

• Create a new array instance from an array of classes or iteratable objects
• arrayLike: pseudo array object or iteratable object that you want to convert to an array
• Mapfn (optional parameter) callback function to be executed for each element in the new array
• this object when thisarg (optional parameter) executes the callback function mapFn
• The return value is a new array instance
```    Array.from(arrayLike, mapFn, thisArg)
```
Published 2 original articles · praised 6 · visited 33

Posted on Thu, 05 Mar 2020 02:35:41 -0800 by cupboy