Question

76

Convert truthy or falsy to an explicit boolean, i.e. to True or False

rated 0 times [ 80] [ 4] / answers: 1 / hits: 104875 / 9 Years ago, wed, july 1, 2015, 12:00:00

I have a variable. Let's call it toto.

This toto can be set to undefined, null, a string, or an object.

I would like to check if toto is set to a data, which means set to a string or an object, and neither undefined nor null, and set corresponding boolean value in another variable.

I thought of the syntax !!, that would look like this:

var tata = !!toto; // tata would be set to true or false, whatever toto is.

The first ! would be set to false if toto is undefined or null and true else, and the second one would invert it.

But it looks a little bit odd. So is there a clearer way to do this?

I already looked at this question, but I want to set a value in a variable, not just check it in an if statement.

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

samir

Add To Favorites

Follow

Total Points: 145

Total Questions: 90

Total Answers: 89

Location: Tokelau

Member since Sun, May 7, 2023

1 Year ago

answered 9 Years ago domeniccolti · Accepted Answer

Yes, you can always use this:

var tata = Boolean(toto);

And here are some tests:

for (var value of [0, 1, -1, 0, 1, cat, true, false, undefined, null]) {

    console.log(`Boolean(${typeof value} ${value}) is ${Boolean(value)}`);

}

Results:

Boolean(number 0) is false

Boolean(number 1) is true

Boolean(number -1) is true

Boolean(string 0) is true

Boolean(string 1) is true

Boolean(string cat) is true

Boolean(boolean true) is true

Boolean(boolean false) is false

Boolean(undefined undefined) is false

Boolean(object null) is false