Why is there no comparison statement in this javascript 'If... Else...' statement

Question

In the following code

var $next =  $active.next().length ? $active.next()
        : $('#slideshow IMG:first');

the part '$active.next().length' doesn't seem to compare anything and I don't understand how the condition is determined to be True or False.

Or is it saying that: if the various $next is equal to $active.next().length then the condition is true?

Answer 1

In javascript any expression can be converted to a truthy or falsy value and hence is valid in a comparison place. The values which are false in javascript are

• false
• 0
• "" (empty string)
• null
• undefined
• NaN

In this case length refers to a numeric value and if it evaluates to 0 then it will be considered falsy. Otherwise it will be truthy

Answer 2

If the length property is equal to 0 or undefined (i.e. $active is not an array), the condition will be false.