what does the following code do in java script:
var x = x || {};
+6
A:
If x is undefined (or null, or any other false value), it becomes an empty object.
Gabe
2010-08-25 05:50:31
+1
A:
Assign x to a new empty object if it is null (undefined, false) or keep it's existing value if not null.
Darin Dimitrov
2010-08-25 05:51:10
+10
A:
|| is the logical OR.
The expression
var x = x OR {};
should become more obvious then.
If x has a falsy value (like null, undefined, 0, ""), we assign x an empty object {}, otherwise just keep the current value. The long version of this would look like
var x = x ? x : {};
jAndy
2010-08-25 05:52:35
excellent answer. i am a c programmer and this didnt make any sense.
jakoh
2010-08-25 06:13:20
If this didn't make any sense for you, then you might also watch out for `!!value` which returns a boolean representing the truthfulness of `value`, very handy at times.
Ivo Wetzel
2010-08-25 06:19:31
Your long version is incorrect: consider the case when x has previously defined and is set to `null`. `var x = x || {};` will redefine x to an object, whereas `var x = (typeof x !== 'undefined') ? x : {};` will not. The paragraph preceding it is correct though.
Tim Down
2010-08-25 15:48:37
@Tim: true, I forgot about the `typeof null === 'object'` enigma.
jAndy
2010-08-25 16:16:31
+1
A:
unless x is defined or assigned a value it will take empty object as default value..
that is,
for example
x = 10
var x = x || {};
output must be
10
if x value not assigned. the output value must be,
undefined
Senthil Kumar Bhaskaran
2010-08-25 05:53:16
A:
if var x is defined then it will be that defined value. Else it will be empty object like [object Object]
e.g. var x = 10; x = x || {}
then it will be 10
var x = x || {};
then it will be [object Object]
Anil
2010-08-25 06:07:04