Surround an object declaration with parenthesis

Question

Curious why the author surrounded object declaration with parenthesis here

rtpg.map.START_KEYS = ({"Key 1":"Value 1", "Key 2":"Value 2", "Key 3":"Value 3", "Key 4":"Value 4"});

why not:

rtpg.map.START_KEYS = {"Key 1":"Value 1", "Key 2":"Value 2", "Key 3":"Value 3", "Key 4":"Value 4"};

for no reason at all? maybe some leftover of what was previously there? — NDM, Aug 05 '13 at 14:14
maybe this is one reason. http://stackoverflow.com/questions/3820488/why-do-we-need-to-add-parentheses-to-eval-json — zs2020, Aug 05 '13 at 14:16
@sza But where is `eval` in this code? And it's not a statement. So none of that SO question is relevant — Ian, Aug 05 '13 at 14:24
@lan I think the parenthesis is used for forcing to convert json to an object though the json self is an object. — zs2020, Aug 05 '13 at 14:27
@sza: [replying to comment #1] Close, but not quite -- following `=`, that _must_ already be an expression, not a statement. — Lightness Races in Orbit, Aug 05 '13 at 14:42
@sza: [replying to comment #2] No, there is no JSON here. JSON is a data interchange format that looks like JavaScript's object literal syntax. This here is simply an object literal. No JSON at all. — Lightness Races in Orbit, Aug 05 '13 at 14:42
@NickyDeMaeyer: I bet you're right; unfortunately that repo only has one revision, so we can't prove it! — Lightness Races in Orbit, Aug 05 '13 at 16:22

score 3 · Accepted Answer · edited May 23 '17 at 10:31

There is no functional difference.

In the case that you emplace JSON text in an eval call to obtain a JavaScript object, you have to use parentheses to disambiguate the resulting expression from a statement, but that is not the case here: the object literal follows a = token and can therefore be parsed only as an expression, with no disambiguation required.

The author has therefore done it out of:

consistency, or
preference, or
ignorance.

score 0 · Answer 2 · answered Aug 05 '13 at 14:40

0

As others have mentioned, there is some value in specifying parenthesis when using eval, but that is not the case here. In this particular code snippet, either way would work exactly the same, so for whatever reason this was just the author's preference.

answered Aug 05 '13 at 14:40

Justin Ethier

131,333
52
229
284

Surround an object declaration with parenthesis

2 Answers2