Weird ternary operator Javascript

Question

I'm trying to understand how ternary operators work and I came across this example:

b.d >= mystr.length && (function1(b, a), a=0);

What does && mean? is it used like an AND operator? how does this translate to regular statement? What does the coma before a=0 mean? Thanks!

&& is AND, as it is in many languages. But also, a duplicate of stackoverflow.com/q/8916679/422184 — LoveAndCoding
– LoveAndCoding, Commented Jan 23, 2012 at 2:18
This is ridiculously unreadable code. Who writes code like that? ಠ_ಠ — Matt Ball
– Matt Ball, Commented Jan 23, 2012 at 2:21

asaelr · Accepted Answer · 2012-01-23 02:22:12Z

2

&& is the AND operator. If the left of it is true, it's evaluate the right side (and return it). The , is the comma operator. (The comma operator evaluate both its sides, left to right, and return the right side). So this code is like:

if (b.d>=mystr.lengh) {
 function1(b,a);
 a=0;
}

(Except that your code return 0)

(My native language is C, so maybe I'm wrong, but I think that in this case, javascript work like C)

answered Jan 23, 2012 at 2:22

asaelr

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Kevin Ennis · Accepted Answer · 2012-01-23 02:33:21Z

2

That's not a ternary.

Also, the comma inside that grouping operator basically ensures that the group will always return the value of the last expression a=0, which is 0.

That example will always evaluate to either false or 0 (which is falsy).

Edit:

For the sake of completeness, here's a ternary operator:

a > b ? functionIfTrue() : functionIfFalse();

It is logically identical to:

if ( a > b ){
    functionIfTrue();
} else {
    functionIfFalse();
}

edited Jan 23, 2012 at 2:33

answered Jan 23, 2012 at 2:23

Kevin Ennis

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2 Comments

user1015551 Over a year ago

Thanks. can you please show me how it would look like a normal statement? What does ">=" mean? isn't that a ternary operator? under what conditions does the function get called?

Kevin Ennis Over a year ago

The >= means "is greater than or equal to". A ternary operator is sort of a shorthand way of writing an if/else statement. In this case, function1 will get called only if mystr.length is less than the value of b.d. If mystr.length is not less than b.d then the rest of the statement after the && doesn't matter, and will therefore not be evaluated.

RobG · Accepted Answer · 2012-01-23 02:27:47Z

0

The && operator is the logical AND operator. It evaluates the expressions from left to right and returns the first falsey value or the value of the last expression..

If it gets to the last expression, it returns its value, whatever that is.

So:

var x = (1 < 2) && ( 4 > 3) && 'fred';

sets x to "fred", whereas:

var y = (1 < 2) && 0 && 'fred';

sets y to 0.

edited Jan 23, 2012 at 2:27

answered Jan 23, 2012 at 2:21

RobG

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