CODEWITHSUNDEEP
javascriptfunctionreturn
DarkMantis
DarkMantis

Reputation: 1516

Return !1 in JavaScript

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

What does this actually mean? Why would you return !1 or return !0?

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
    }
}

Upvotes: 21

Views: 11144

Answers (3)

Lochan Rao Pawar
Lochan Rao Pawar

Reputation: 23

Here the code it is verifying:

  • to return nothing or do nothing on these cases: "case 1", "case true", "case yes", "case y", "Case 1"
  • and when the case is: "case !0" return "true"
  • when none of the above cases are been satisfied by default, it returns "false"

Upvotes: -4

Bakudan
Bakudan

Reputation: 19492

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.

Upvotes: 23

spender
spender

Reputation: 120498

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

Upvotes: 11

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