Is there a simple way to make these two lines into a one-liner?

Question

Here are the two lines:

pixels[x-left] = {};
pixels[x-left][y] = true;

It would greatly allow me to clean up some code if the two could be combined into a single expression.

My first attempt looked something like this:

pixels[x-left] = { y: true };

However the letter y is being used as the index instead of the value of y, which is not OK.

This is an often asked question. Duplicate with the most upvotes I could find: [Using a variable for a Javascript object key](http://stackoverflow.com/questions/2274242/using-a-variable-for-a-javascript-object-key) — Bergi, Apr 15 '13 at 00:22

Fabrício Matté · Accepted Answer · 2013-04-19T21:44:47.233

3

I'll start right off saying that Bergi's solution should be preferred, but in case you don't mind killing your code's readability:

(pixels[x-left] = {})[y] = true;

This works as an assignment expression returns the assigned value (in this case, a reference to the assigned object).

edited Apr 19 '13 at 21:44

answered Apr 15 '13 at 00:16

Fabrício Matté

Aw, nice :-) Of course that changes the statement value, but it shouldn't matter – Bergi Apr 15 '13 at 00:20
There's a semi-colon after the statement and I hope it is not part of another expression so yes, it assumes the expression's return value isn't significant. `=]` – Fabrício Matté Apr 15 '13 at 00:25
It's not "pretty", but it's what I was looking for, thank you! – Joncom Apr 15 '13 at 00:47

Bergi · Answer 2 · 2013-04-15T00:24:51.527

2

No, there is ~~not~~ no clean one*. Any property name in an object literal is interpreted literally.

One way out would be some kind of helper function, like

Object.set = function(o, p, v) { o[p] = v; return o; };

pixels[x-left] = Object.set({}, y, true);

but then everybody reading your code would need to know about Object.set.

_{* After @Fabricio's answer I can't state "no possibility" any more :-)}

edited Apr 15 '13 at 00:24

answered Apr 15 '13 at 00:09

Bergi

+1 for not murdering Antarctica's seals. `=]` And rofl at the mention. `xD` – Fabrício Matté Apr 15 '13 at 00:26

2 Answers2