16. Truthy and Falsy

Truthy and Falsy

Every value in JavaScript has an inherent boolean value. When that value is evaluated in the context of a boolean expression, the value will be transformed into that inherent boolean value.

The paragraph above is pretty dense with information. You should probably re-read it again! ☝️

Falsy values

A value is falsy if it converts to false when evaluated in a boolean context. For example, an empty String "" is falsy because, "" evaluates to false. You already know if…else statements, so let's use them to test the truthy-ness of "".

if ("") {
    console.log("the value is truthy");
} else {
    console.log("the value is falsy");
}

Returns: "the value is falsy"

Here’s the list of all of the falsy values:

1. the Boolean value false

• the null type
• the undefined type
• the number 0
• the empty string ""
• the odd value NaN (stands for "not a number", check out the NaN MDN article)

That's right, there are only six falsy values in all of JavaScript!

Truthy values

A value is truthy if it converts to true when evaluated in a boolean context. For example, the number 1 is truthy because, 1 evaluates to true. Let's use an if…else statement again to test this out:

if (1) {
    console.log("the value is truthy");
} else {
    console.log("the value is falsy");
}

Returns: "the value is truthy"

Here are some other examples of truthy values:

true
42
"pizza"
"0"
"null"
"undefined"
{}
[]

Essentially, if it's not in the list of falsy values, then it's truthy!