Use of arrow function

The arrow function is ES6 Then add a method of writing functions , And it's more concise than function expressions .

• Arrow functions are not bound this、arguments attribute ;
• The arrow function cannot be used as Constructors To use

Writing form of arrow function

• () The parameters of the function
• {} The body of the function  

nums.forEach((item, index, arr)=>{

})

Writing optimization of arrow function

Optimize one ： If there is only one parameter () It can be omitted

nums.forEach(item => {})

Optimization II ： If there is only one line of code in the body of the function , Then you can omit the braces

And the return value of this line of code will be used as the return value of the whole function

nums.forEach(item => console.log(item))
nums.filter(item => true)

Optimize three ： If the function body returns only one object , So you need to add... To this object ()

var foo = () => {
    return { name: "abc" }
}

var bar = () => ({name: "abc"})

Case study ： Use the arrow function to output the even sum of squares in an array

var nums = [20, 40, 11, 22, 45, 36, 89]
      var result = nums.filter(item => item % 2 === 0)
                       .map(item => item ** 2)
                       .reduce((preValue, item)=> preValue + item)
                      
      console.log(result)