freeCodeCamp/guide/english/javascript/truthy-values/index.md

title
Truthy Value

Description

A truthy value is a value that translates to true when evaluated in a Boolean context.

All values are truthy unless they are defined as falsy (i.e. except for false, 0, "", null, undefined and NaN).

Checking for Truthy Values on Variables

It is possible to check for a truthy value in a variable with a simple conditional:

if (variable) {
  // When the variable has a truthy value the condition is true.
}

You can also get the boolean value of a variable by using the bang operator (!) twice:

!!variable // When the variable is truthy, a double bang (!!) will evaluate to the Boolean true.

Interesting JavaScript Rules concerning Truthy Values

These Are Interesting Truthy Values

• '0' (a string containing a single zero)
• 'false' (a string containing the text “false”)
• [] (an empty array)
• {} (an empty object)
• function(){} (an “empty” function)

Comparing Interesting Truthy Values

• false, zero and ''(empty strings) are all equivalent.
• null and undefined are equivalent to themselves and each other but nothing else.
• NaN is not equivalent to anything – including another `NaN!
• Infinity is truthy – but cannot be compared to true or false!
• An empty array([]) is truthy – yet comparing with true is false and comparing with false is true?!

More Information

See also: falsy | MDN