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  • Assigning to empty array/object literals

Assigning to empty array/object literals

# Michael Day (15 years ago)

Firefox 3.6.8 supports the following expressions:

[] = 3;

and:

{} = 3;

Although this object-literal version will trigger a syntax error at block scope, and so needs to be written like this:

x = ({} = 3);

In any case, shouldn't both of these expressions be early syntax errors, as the left hand side can never be a reference?

For comparison, non-empty array and object literals throw an error:

[1] = 3; // SyntaxError x = ({foo: 1} = 3); // SyntaxError

Bug in Firefox? Or subtlety of the spec that's gone over my head? :)

Best ,

Michael

# Dmitry A. Soshnikov (15 years ago)

On 10.08.2010 9:21, Michael Day wrote:

Hi,

Firefox 3.6.8 supports the following expressions:

[] = 3;

and:

{} = 3;

Although this object-literal version will trigger a syntax error at block scope, and so needs to be written like this:

x = ({} = 3);

In any case, shouldn't both of these expressions be early syntax errors, as the left hand side can never be a reference?

For comparison, non-empty array and object literals throw an error:

[1] = 3; // SyntaxError x = ({foo: 1} = 3); // SyntaxError

Bug in Firefox? Or subtlety of the spec that's gone over my head? :)

Destructuring (or, regarding JS -- "Non-strict pattern matching").

[a] = [3];

a; // 3

{a: b} = {a: 3, x: 4};

b; // 3

{a: c} = {};

c; // undefined

[x, y] = {not_an_array: 42}; // OK

[x, [y, z]] = {nor_here: 99}; // TypeError

esdiscuss/2010-July/011617

# Michael Day (15 years ago)

Destructuring (or, regarding JS -- "Non-strict pattern matching").

Thanks, I was fooled by the fact the left hand side was empty :)