dandelany on ES6 in Depth: Destructuring

I've been writing ES6 with Babel for a couple of months now, and I've fallen in love with destructuring - it's my second favorite part, besides arrow functions. My only complaint, having run into this a few times in real code, is that you can only use destructuring with assignment, not with existing variables. So this works:

  let myThing = {a: 4};
  let {a} = myThing;

But this does not:

  let a = 5;  
  let myThing = {a: 4};
  {a} = 5;

I understand there are some problems of ambiguity here, but it seems to me this could be made to work somehow?

loganfsmyth 11y

Yeah, I wish that were handled better too. Since the parser is expecting a statements, it parses it like

As in, a block with just an "a" in it, followed by an assignment to nothing, which throws an syntax error.

You can however do

    ({a} = 5);

to make the parser switch to expecting a destructuring pattern instead of an block statement.

dandelany 11y

Whoops, my last line contains a major typo and should read `{a} = myThing;`. And you've dutifully carried over my typo to your example :D

But regardless, the corrected version of your example: `let a; ({a} = {a:5});` works like a charm and is very handy! Thanks for the tip!

lucian1900 11y

At least with let you can reliably shadow the previous binding, which in most cases will be equivalent.

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