Destructuring assignment cause error: "unexpected token ="

Question

let's say I call use this syntax in es6:

let a, b;

{a, b} = { a: 100, b: 300 };

the code will run without error;

but let's rewrite is like this:

function fn() {
    return { a: 100, b: 200 }
}

let a, b;

{ a, b } = fn();

when I run the code above, it says unexpected token "="; I am a little confused, what is the difference?

it doesn't matter where it runs, you can try any of the enviroment you mentioned — 碳60, Jul 02 '18 at 12:22
None of your examples work for me, but if I do instead `var {a, b} = fn()` (note var instead of let) it works (and if I put both in the same line) — hellow, Jul 02 '18 at 12:34
@hellow yes that will work too, see my answer below. let vs. var not making a difference here - having on same line is. — joknawe, Jul 02 '18 at 12:43

joknawe · Accepted Answer · 2018-07-02T12:35:26.973

24

Add round braces: ({ a, b } = fn());

From Mozilla documentation:

The round braces ( ... ) around the assignment statement is required syntax when using object literal destructuring assignment without a declaration.

{a, b} = {a: 1, b: 2} is not valid stand-alone syntax, as the {a, b} on the left-hand side is considered a block and not an object literal.

However, ({a, b} = {a: 1, b: 2}) is valid, as is var {a, b} = {a: 1, b: 2}

edited Jul 02 '18 at 12:35

answered Jul 02 '18 at 12:29

joknawe

@碳60 yes a very good resource indeed. Please accept this answer if you found it helpful. Thanks. – joknawe Jul 02 '18 at 13:10
Sure thing, when I earned 15 reputations, I will come back and accept your answer! – 碳60 Jul 02 '18 at 13:19
@碳60 now you do ;) – hellow Jul 02 '18 at 13:24
Done! So excited! – 碳60 Jul 02 '18 at 13:30
@joknawe sorry, I did not realized that I have to click the accept flag – 碳60 Jul 05 '18 at 06:20
FYI - You can also use `let, var, const` without the braces around the entire statement and it will work too. – 4Z4T4R Oct 04 '20 at 06:07

score 0 · Answer 2 · answered Apr 04 '21 at 14:48

0

Wrap the object assignment in parenthesis

({a ,b} = fn());

answered Apr 04 '21 at 14:48

sai surya madhav

score -3 · Answer 3 · answered Jul 02 '18 at 11:51

-3

Use a,b instead of {a,b}:

let a, b;
a,b = { a: 100, b: 300 };


function fn() {
    return { a: 100, b: 200 }
}

let a, b;
a,b = fn();

answered Jul 02 '18 at 11:51

Rupinder

4

it is not, in your solution, a is undefined, and b is { a: 100, b: 200 }, that is not my expectation – 碳60 Jul 02 '18 at 12:20

3 Answers3