returning with &&

Question

What does it mean to return a value with &&?

else if (document.defaultView && document.defaultView.getComputedStyle) {      // It uses the traditional ' text-align' style of rule writing,      // instead of textAlign     name = name.replace(/([A-Z]) /g, " -$1" );     name = name.toLowerCase();     // Get the style object and get the value of the property (if it exists)     var s = document.defaultView.getComputedStyle(elem, " ") ;     return s && s.getPropertyValue(name) ; 

Answer 1

return a && b means "return a if a is falsy, return b if a is truthy".

It is equivalent to

if (a) return b; else return a; 

Answer 2

The logical AND operator, &&, works similarly. If the first object is falsy, it returns that object. If it is truthy, it returns the second object. (from https://www.nfriedly.com/techblog/2009/07/advanced-javascript-operators-and-truthy-falsy/).

Interesting stuff!

EDIT: So, in your case, if document.defaultView.getComputedStyle(elem, " ") does not return a meaningful ("truthy") value, that value is returned. Otherwise, it returns s.getPropertyValue(name).