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>