CODEWITHSUNDEEP
javascript
Nikita Shchypylov
Nikita Shchypylov

Reputation: 367

Why do we use [].join here?

Why do we use [].join() in this way?

function printArgs() {
    arguments.join = [].join; 
    var argStr = arguments.join(':'); 
    alert( argStr );
}
printArgs(1, 2, 3);

Upvotes: 4

Views: 87

Answers (2)

Manasov Daniel
Manasov Daniel

Reputation: 1378

Because arguments object is Array-like object but it is not real array and it doesn't have array properties (like join in your example) except .length. So in your code you are copying .join method from array to arguments object.

Upvotes: 4

brk
brk

Reputation: 50291

The argument object is an local variable array like object which is available in all functions.

So arguments.join = [].join; is creating a new array and on which you can use all methods that are available in js array.

Therefore var argStr = arguments.join(':'); will return 1:2:3

var argStr = arguments.join();      // assigns '1,2,3' to argStr 
var argStr = arguments.join(' + '); // assigns '1 + 2 + 3' to argStr
                          // ^ ^       Note empty space here & in assigned value
var argStr = arguments.join('');  // assigns 123 to argStr

Upvotes: 0

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