return !1 in javascript

Question

I have just come across a function in javascript which has return !1

I was just wondering what this actually meant?

Why would you return !1 or return !0

Could someone please explain what it means please?

Here is the function that I came across:

function convertStringToBoolean(a) {     typeof a == "string" && (a = a.toLowerCase());     switch (a) {     case "1":     case "true":     case "yes":     case "y":     case 1:     case !0:         return !0;     default:         return !1     } } 

Thanks In advance!

Answer 1

In immediate response to your question:

• return !1 is equivalent to return false
• return !0 is equivalent to return true

In the specification - 11.4.9 Logical NOT Operator - it states that when you place an exclamation mark ! in front, the result is evaluated as Boolean and the opposite is returned.

Example:

var a = 1, b = 0; var c = a || b; alert("c = " + c + " " + typeof c); // here typeof c will be "number"  a = !0, b = !1; c = a || b; alert("c = " + c + " " + typeof c); // here typeof c will be "boolean" 

I mostly see this in a code passed through Google's JS optimiser. I think it is mostly done to achieve shortness of the code.

It is often used when a strictly Boolean result is needed - you may see something like !!(expression). Search in jQuery, for example.

Answer 2

This seems to be a particularly silly way of returning true or false