Spread operator in 'new' expressions support for ES5?

I've found that #1931 supports this only for ES6, but it seems ES5 also can do this in any way.

var arguments = [1, 2, 3, 4, 5];
new Array(...arguments);

This can be converted to ES5:

// Thanks to: http://stackoverflow.com/a/14378462/2460034
var arguments = [1, 2, 3, 4, 5];
new (Array.bind.apply(Array, [null].concat(arguments)));
// Result: [1, 2, 3, 4, 5]

Seems reasonable enough.

Approved. Be sure to handle the case where the operand to new is a computed expression that needs to be cached in a temporary variable.

I'm almost done with a PR on this one. Though there are one issue with the type checker:

interface ObjectWithSpreadMethod {
    spreadMethod(x: number, y: number, ...z: string[]);
}

var spread: string[];
var objectWithSpreadMethod: ObjectWithSpreadMethod;

new objectWithSpreadMethod.spreadMethod(1, 2, "string");
new objectWithSpreadMethod.spreadMethod(1, 2, ...spread);
new objectWithSpreadMethod.spreadMethod(1, 2, ...spread, "string");

Isn't it correct TS code above? Why can't I do new objectWithSpreadMethod.spreadMethod on a method?

Shall I correct this behavior?

Playground:
http://www.typescriptlang.org/Playground#src=interface%20ObjectWithSpreadMethod%20%7B%0D%0A%20%20%20%20spreadMethod(x%3A%20number%2C%20y%3A%20number%2C%20...z%3A%20string%5B%5D)%3B%0D%0A%7D%0D%0A%0D%0Avar%20spread%3A%20string%5B%5D%3B%0D%0Avar%20objectWithSpreadMethod%3A%20ObjectWithSpreadMethod%3B%0D%0A%0D%0Anew%20objectWithSpreadMethod.spreadMethod(1%2C%202%2C%20%22string%22)%3B%0D%0Anew%20objectWithSpreadMethod.spreadMethod(1%2C%202%2C%20...spread)%3B%0D%0Anew%20objectWithSpreadMethod.spreadMethod(1%2C%202%2C%20...spread%2C%20%22string%22)%3B%20

Seems like it should be typed like this:

interface ObjectWithSpreadMethod {
    spreadMethod: {
        new (x: number, y: number, ...z: string[])
    };
}

Alternatively:

interface ObjectWithSpreadMethod {
    spreadMethod(x: number, y: number, ...z: string[]): void;
}

The code as written has spreadMethod returning any, which is not a valid invocation target for new.

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) Ok thanks, I will land a PR later.

Tingan Ho (@tinganho)

thanks Tingan Ho (@tinganho)!

Does this seem to just be a happy coincidence with Array? Using this technique with my own TS classes doesn't work.

Seems as if it really is impossible. According to MDN --

Apply for new

Example: In ES5 it is not possible to compose new with apply (in ES5 terms apply does a [[Call]] and
not a [[Construct]]). In ES6 the spread syntax naturally supports this.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator

Further reading into the ES6 standard:

The Array constructor is the %Array% intrinsic object and the initial value of the Array property of the global object. When called as a constructor it creates and initializes a new exotic Array object. When Array is called as a function rather than as a constructor, it also creates and initializes a new Array object. Thus the function call Array(…) is equivalent to the object creation expression new Array(…) with the same arguments.

Which tells me that using something that does a [[Call]] with an array (.apply() or .call()) also has the same effect as a [[Construct]].

I'm fine with allowing this behavior in this case, so maybe allowing for a warning to be emitted instead of an error, or for special casing the errors to give a hint to the programmer as to why a program isn't behaving as expected might be a useful thing.

mdcone

mdcone could you share your classes? I tested it with TS classes and it seems to work for me.

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Spread operator in 'new' expressions support for ES5? #2369

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Spread operator in 'new' expressions support for ES5? #2369

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RyanCavanaugh commented on Mar 17, 2015

RyanCavanaugh commented on May 4, 2015

tinganho commented on May 7, 2015

RyanCavanaugh commented on May 7, 2015

tinganho commented on May 7, 2015

mhegazy commented on May 18, 2015

mdcone commented on Aug 20, 2015

tinganho commented on Aug 20, 2015

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