Menu
In javascript, when using an if statement with multiple conditions to test for, does javascript test them all regardless, or will it bail before testing them all if it's already false?
For example:
a = 1 b = 2 c = 1 if (a==1 && b==1 && c==1) Will javascript test for all 3 of those conditions or, after seeing that b does not equal 1, and is therefore false, will it exit the statement?
I ask from a performance standpoint. If, for instance, I'm testing 3 complex jQuery selectors I'd rather not have jQuery traverse the DOM 3 times if it's obvious via the first one that it's going to return FALSE. (In which case it'd make more sense to nest 3 if statements).
ADDENDUM: More of a curiosity, what is the proper term for this? I notice that many of you use the term 'short circuit'. Also, do some languages do this and others dont?
203
You can use the logical AND (&&) and logical OR (||) operators to specify multiple conditions in an if statement. When using logical AND (&&), all conditions have to be met for the if block to run.
Using either “&&” or “||” i.e. logical AND or logical OR operator or combination of can achieve 3 conditions in if statement JavaScript.
Use two if statements if both if statement conditions could be true at the same time. In this example, both conditions can be true. You can pass and do great at the same time. Use an if/else statement if the two conditions are mutually exclusive meaning if one condition is true the other condition must be false.
We can also write multiple conditions inside a single if statement with the help of the logical operators && and | | . The && operators will evaluate if one condition AND another is true. Both must be true before the code in the code block will execute.
The && operator "short-circuits" - that is, if the left condition is false, it doesn't bother evaluating the right one.
Similarly, the || operator short-circuits if the left condition is true.
EDIT: Though, you shouldn't worry about performance until you've benchmarked and determined that it's a problem. Premature micro-optimization is the bane of maintainability.
156
From a performance standpoint, this is not a micro-optimization.
If we have 3 Boolean variables, a, b, c that is a micro-optimization.
If we call 3 functions that return Boolean variables, each function may take a long time, and not only is it important to know this short circuits, but in what order. For example:
if (takesSeconds() && takesMinutes()) is much better than
if (takesMinutes() && takesSeconds()) if both are equally likely to return false.
36
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
