Truthy and falsy values in JavaScript

Last updated: September 27, 2022.

The terms truthy and falsy refers to the Boolean value type – true or false – that a value is converted to in a logical statement.

In total, there are seven falsy values in JavaScript:

• Numeric 0
• BigInt 0n
• The value null
• The non-value undefined
• The Boolean value false
• Not a number: NaN
• Empty string: ""

All other values are truthy!

Truthy and falsy in logical statements

Truthy and falsy values are important in logical statements, such as if…else conditionals.

The if condition accepts a true or false Boolean value or converts whatever is passed into it to true or false. If the value is true, the statement is run.

This means that if a falsy value is passed in, the if statement will not run:

if (2022) {
    console.log("With truthy value"); // Logs message to console
}

if (null) {
    console.log("With falsy value"); // No output
}

if (undefined) {
    console.log("With falsy value"); // No output
}

if ("JavaScript") {
    console.log("With truthy value"); // Logs message to console
}

In practice, the conversion of values to truthy or falsy is useful for only running an if statement if a process has resulted in a value being assigned to a variable:

const userInput1 = "Some comments";
const userInput2 = null;

if (userInput1) {
    console.log("Comments = " + userInput1)
} else {
    console.log("User did not enter any comments")
}
// Output: Comments = Some comments

if (userInput2) {
    console.log("Comments = " + userInput2)
} else {
    console.log("User did not enter any comments")
}
// Output: User did not enter any comments

---