Spread operator ES5 equivalent

Question

Below is the code I am trying to convert to ES5 for IE compatibility.

$.when(...requests).then(function(...responses) {
 // More code goes here
}

So far I could convert it to the below and it works well, but I still couldn't replace the then part.

$.when.apply(null, requests).then(function(...responses) {
 // More code goes here
}

Any suggestion would be really appreciated.

• VLAZ: Why not transpile the code?
• VLAZ: Also, you seem to only be asking about rest parameter syntax: function(...responses). Only $.when(...requests) is using spread.

Answer 1

There is arguments:

$.when.apply(null, requests).then(function() {
 var responses = [].concat.apply([], arguments); // Get a standard array from arguments object
 // More code goes here
}

As a disclaimer I quote MDN on the use of arguments:

If you're writing ES6 compatible code, then rest parameters should be preferred.

So when you don't have ES6 support (which seems to be your case), then using arguments is fine, but otherwise you should use the spread syntax in the function parameter list.

• Parag Kadam: Thanks for the answer, it seems to work with a little tweak -> var responses = [].concat(arguments)[0];.
• trincot: Indeed. I corrected this in the answer. It should in fact use apply, otherwise there is no conversion to standard Array. But that conversion is optional. If you don't use Array methods like .forEach, ...etc, you can just use responses = arguments or use arguments directly.