what does line mean: var DYN_WEB = DYN_WEB || {}; in js?

Question

var DYN_WEB = DYN_WEB || {};

I saw above code in one js file

Question:

what does this mean?

score 6 · Accepted Answer · answered Jun 29 '13 at 07:21

6

if DYN_WEB is not null it will take the value already set for DYN_WEB else assign an empty object to it.

answered Jun 29 '13 at 07:21

codetantrik

315
2
9

This also applies for other values that evaluate to false. – Gumbo Jun 29 '13 at 07:24

score 1 · Answer 2 · answered Jun 29 '13 at 07:24

1

This is shorthand for

if ( ! DYN_WEB ) {
  DYN_WEB = {}
}

or

var DYN_WEB = DYN_WEB ? DYN_WEB : {}

answered Jun 29 '13 at 07:24

Yang

8,580
8
33
58

0xc0de · Answer 3 · 2013-06-29T08:00:12.093

0

it means if the variable DYN_WEB has a value which is evaluated to binary true, then keep that value, otherewise assign {} to it. The latter will happen if the previous value of the variable is 'falsy' ie. one of the false, null, undefined, NaN, 0, "", [] or {} and in case it's not defined.

edited Jun 29 '13 at 08:00

answered Jun 29 '13 at 07:50

0xc0de

8,028
5
49
75

what does line mean: var DYN_WEB = DYN_WEB || {}; in js?

3 Answers3