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Comment by rplnt | Hacker News Reader

Looking at documentation.. does this only work on lists (or list like object)? I.e. you can't "expand" a k:w object? Or is there another operator for this? Example:

    function foo(a=1, b=2, c=3) { return a * b * c;}
    dict = {'b': 4, 'c': 6};
    foo(...dict);

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Technically, the spread operator works with iterables [1]. If you wanted to spread an object `obj`you'd need to define `obj[Symbol.iterator]` [2].

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... [2] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

Yes and no.

You can still do something like:

    foo(... Object.keys(dict).map(name => dict[name]))

(Maybe someday you might be able to use Object.values() to achieve the exact same thing without needing to use .map)

However, the spread operator doesn't match the argument names to the object names. So the above call would mean the following:

    foo(4, 6)

And not what you'd like:

    foo(undefined, 4, 6)

However, note that you can rest an object too:

    let x = { a : 1, b : 2, c : 3 };
    let { a, ... rest } = x;

    console.log( ... rest ); // { b : 2, c : 3 }

There is a proposal for this but I'm not sure what stage that's in

Stage 2

https://github.com/tc39/ecma262 https://github.com/sebmarkbage/ecmascript-rest-spread

You still have to simulate named arguments with an object:

    const foo = ({ a = 2, b = 2, c = 3 } = {}) => a * b * c;
    const dict = {b: 4, c: 6};

    foo(); // 12
    foo(dict); // 48

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