1342837 - Destructuring second parameter with default value throws SyntaxError

Status: RESOLVED DUPLICATE of bug 1204024

(Core :: JavaScript Engine, defect)

Description

[Andrew Li]

User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36

Steps to reproduce:

The following code, tested in Firefox 50.0.2 and 51.0.1:

    const foo = (x, { y = "bar" }) => console.log(x, y);
    foo("foo", {});


Actual results:

The actual result was a SyntaxError:

    SyntaxError: missing : after property id

Seems like it's mistaking { y = "bar" } as an object literal and not a destructured parameter with a default value. Without the default value it works fine.


Expected results:

I would have expected the following result:

    foo("foo", {}); //foo bar

I also tried:

    const foo = (x, { y: y } = { y: "bar" }) => console.log(x, y);

As suggested here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters#Destructured_parameter_with_default_value_assignment but it did not produce the desired result. But the following:

    const foo = (x, { y = "bar" } = {}) => console.log(x, y);

Works perfectly.

Comment 1

[Tooru Fujisawa [:arai]]

it's fixed in bug 1204024 (firefox 52)