Why Use: Expression && Expression ... in code?

Question

What is the purpose of the following line of JavaScript?

for (p in d) d.hasOwnProperty(p) && h.push([p, d[p]]);

From what I can see it doesn't change nothing. Does it mean: If d has the property p AND p and d[p] can be pushed onto h than the expression is true? Thus, the h.push will never happen if d does not have the property p.

This is exactly why I hate concise code.

Your interpretation is correct, except that the being `true` part is not important here. — Jongware, Dec 28 '13 at 23:50
That code is hardly concise. It might be terse, but definitely not concise. — bevacqua, Dec 28 '13 at 23:54
My vocabulary sucks. My English literature is poor. This is why I studied Computer Science and not Shakespeare. — Torra, Dec 29 '13 at 00:08

score 1 · Accepted Answer · answered Dec 28 '13 at 23:50

1

The idea is that when using &&, the left part is evaluated first. If, and only if, its return value is true, is the right part evaluated at all.

So, for each iteration, d.hasOwnProperty(p) is evaluated first. If the result is true, then h.push([p, d[p]]) is evaluated.

answered Dec 28 '13 at 23:50

Eran Boudjnah

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Thanks! Threw me off for a good 5 minutes this did. – Torra Dec 28 '13 at 23:51

score 0 · Answer 2 · answered Dec 28 '13 at 23:54

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It's a shortcut of

for (p in d) if (d.hasOwnProperty(p)) h.push([p, d[p]]);

answered Dec 28 '13 at 23:54

Oriol

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Why Use: Expression && Expression ... in code?

2 Answers2