JavaScript: list of implicit true/false values
I got tired of sometimes wondering whether I could use a particular JavaScript value effectively in a conditional statement…
For instance, if I’m in the middle of a block of JS code, and am not 100% sure what the value of a variable will be, is it safe to say:
if (foo)
or do I need to explicitly look at the value of foo, like:
if ((typeof foo != 'undefined') &&
(foo != null) &&
(foo != ''))
So, I took a little time one day, recently, and checked how various values are evaluated in JavaScript. I believe I gathered this info using IE6. Hopefully that fact is not important. Might be worth checking in Firefox one of these days, just to be sure.
| false | false |
| 0 | false |
| 0.0 | false |
| null | false |
| ” | false |
| undefined | false |
| NaN | false |
| true | true |
| Infinity | true |
| ‘ ‘ | true |
| 1 | true |
| -1 | true |
| 2 | true |
| -2 | true |
| 0.1 | true |
| ‘0′ | true |
| ‘1′ | true |
| ‘-1′ | true |
| ‘null’ | true |
| ‘true’ | true |
| ‘false’ | true |
| ‘TRUE’ | true |
| ‘FALSE’ | true |
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December 6th, 2006 at 11:31 pm
A handy list - thanks!