Detailed explanation of the new array methods in JavaScript es6

1. forEach()

Traverse the array without return. Even if there is return, no value will be returned and the original array will be affected.

callback parameters

value -- the value of the current index

index --index

arr -- original array

		let arr = ["a", "b", "c", 1, 2, 3];
        
        arr.forEach((value, index, arr) => {
            console.log(value, index, arr);
        })

Output:

2. arr.filter()

Filter an array and return an array that meets the requirements

callback parameters:

value -- the value of the current index

index --index

let arr = [1,2,3,4,5]
let arr1 = arr.filter( (value, index) => value%2 === 0)
console.log(arr1) // [2, 4]

3. arr.every()

According to the judgment condition, whether all elements of the array meet the requirements, if so, return true

callback parameters:

value -- the value of the current index

index --index

let arr = [1,2,3,4,5]
let arr1 = arr.every( (value, index) =>value<2)
console.log(arr1) // false
let arr2 = arr.every( (value, index) =>value<6)
console.log(arr2) // true

4. arr.map()

Map an array (traverse the array), and return a new array.

callback parameters:

value -- the value of the current index

index --index

array -- the original array

let arr = [1,2,3,4,5]
arr.map( (value,index,array)=>{
        value = value * 2
        console.log(`value:${value} index:${index} array:${array}`)
})   
console.log(arr)

result:

var arr1 = [1,2,3,4]; 
var res1 = arr1.map((item,index,arr)=>{ 
 item = item * 3; 
 return item; 
})
console.log(arr1); // [1,2,3,4]
console.log(res1); // [3,6,9,12]

5. arr.some()

According to the judgment condition, whether one of the elements of the array meets the condition, if one meets the condition, return true

callback parameters:

value -- the value of the current index

index --index

let arr = [1,2,3,4,5]
let arr1 = arr.some( (value, index) => value < 3)
console.log(arr1) // true
let arr2 = arr.some( (value, index) => value > 6)
console.log(arr2) // false

Summarize

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