Hacker News Reader

Comment by ffn | Hacker News Reader

var [wtf] = NaN; console.log(wtf); // undefined

I don't know about you, but this sensibly gives a TypeError when I did it in my console on Firefox 38. Please let this article be more dated than my firefox browser, because making NaN auto-coerce into an iterator sounds incredibly stupid.

View on HN

I suspect it's just accessing NaN[0]. Either form of property access ([] or .) implied coercion to object (not iterable) in ES5. It makes sense that destructuring would build on that behavior.

Array destructuring doesn't use [0] access. It iterates the right-hand side. On the one hand, that means that trying to array-destructure NaN does in fact throw. On the other hand, it means you can array-destructure a generator, which is a very desirable thing to be able to do.

That looks like a typo in the example. This code:

  var {wtf} = NaN;

would set wtf to undefined, for the reasons described in the article, since it would end up doing (NaN)["wtf"]. But trying to destructure NaN into an array should throw an exception.

    var temp = NaN;
    var wtf = temp[0];
    console.log(wtf); //undefined

What else would you expect it to be? JavaScript in general guards against throwing errors as much as possible... I'd much rather see this behavior in practice than having to put extra try/catch blocks everywhere... Not to mention what this would do to async code.

Reply on news.ycombinator.com