[ES6] 23. Rest Parameters & Spread Parameters

Rest Parameters:

 

In ES5, when you don't know how many paramters will be passed in, you can use arguments:

let sum = function(){
    let result = 0;
    for(let i = 0; i < arguments.length; i++){
        result += arguments[i];
    }
    return result;
}

let result = sum(1,2,3);

 

In ES6, you can use Rest params:

let sum = function(...numbers){
    
    let result = 0;
    for(let i = 0; i < numbers.length; i++){
        result += numbers[i];
    }
    return result;
};

 

describe("rest paramters", function(){

    it("is like varargs", function(){
    
        let doWork = function(name, ...numbers){
        
            let result = 0;
            numbers.forEach(function(n){
                result += n;
            });
            
            return result;
        };
        
        let result = doWork("Scott", 1,,2,3);
        expect(result).toBe(6);
    });
});

 

...Spread:

It looks the same as Rest Parameters, Spread uses to spread an array.

it("should sum up", function(){
    let doWork = function(x,y,z){
        return x+y+z;
    };
    
    expect(doWork(...[1,2,3])).toBe(6);
});

 

<!DOCTYPE html>
<html>
  <head>
    <script data-require="traceur@*" data-semver="0.0.0-20140302" src="https://traceur-compiler.googlecode.com/git/bin/traceur.js"></script>
    <script>
     traceur.options.experimental = true;
    </script>
    <script data-require="traceur@*" data-semver="0.0.0-20140302" src="https://traceur-compiler.googlecode.com/git/src/bootstrap.js"></script>
    <link rel="stylesheet" href="style.css" />
    <script src="script.js"></script>
  </head>

  <body>
      <script type="module">
            let a = [4,5,6];
            let b = [1,2,3, ...a, 7,8,9];
            document.write(b); //1,2,3,4,5,6,7,8,9
      </script>
  </body>
</html>

 

posted @ 2015-05-01 18:40  Zhentiw  阅读(262)  评论(0)  编辑  收藏  举报