Allow ArrayLike as a spread source

[iby]

When trying to pass caller arguments to another function with ...arguments the compiler complains with Type 'IArguments' is not an array type. Version 1.8.9.

[jwbay]

The arguments object is not an array type (though it resembles one), so the compiler error seems correct. Accept the arguments with a rest operator and they'll get converted to an array.

function foo(...args) {
   bar(...args);
}

[iby]

Now when you say it, I remember looking it up a dozen times now… Still, that functionality would be natural, especially given that apply can be used directly with arguments.

[iby]

@mhegazy I wasn't asking a question. This works in javascript, typescript fails to compile. arguments is not an array, it's a fact, but it should be compatible with the spread operator.

[mhegazy]

it is not an array. quoting MDN:

The arguments object is an Array-like object corresponding to the arguments passed to a function.

it goes on to say:

The arguments object is not an Array. It is similar to an Array, but does not have any Array properties except length. For example, it does not have the pop method. However it can be converted to a real Array

so,

function f() {
  arguments.push(0);          // Runtime error: Uncaught TypeError: arguments.push is not a function(…)
  arguments.indexOf(0);       // Runtime error: Uncaught TypeError: arguments.indexOf is not a 
  Array.isArray(arguments);   // false
}
f(1,2);

[iby]

We're having a miscommunication. I am not saying it's an array, I'm stating the opposite, that it is not array, but it should be compatible with the spread operator.

function foo(){
    console.log(...arguments);
}

foo('bar', 'baz');

This throws a compile error, but produces a working code. Naturally arguments would be expected to work with the spread operator.

[mhegazy]

i see.

well. some of the transformation on a spread uses slice. which does not exist. in theory we can allow ArrayLike, and call Array.prototype.slice.apply(v) instead of v.slice

[mhegazy]

updating the title.

[kitsonk]

It isn't valid ES6 syntax:

'use strict';

function bar() {
  console.log(arguments);
}

function foo() {
  bar.call(this, ...arguments);
}

foo('bar', 'qat');

It fails in Firefox (but not in Chrome or Edge) and so would have to be transformed even when targeting ES6 with little or no value. It was the "magic" behaviours of arguments was a big part of the value of the spread/rest operator in the first place.