Truthy and Falsy

In JavaScript, you do not need to explicitly convert a value to a boolean before using it in a conditional statement like an if block. JavaScript automatically evaluates values as either “truthy” or “falsy”.

Truthy Values

A truthy value is one that evaluates to true when encountered in a boolean context.

if ("hello") {
  console.log("hello is truthy");
}
if (42) {
  console.log("42 is truthy");
}

Common truthy values include:

• true
• 42 (Any number that is not 0)
• "hello" (Any non-empty string)
• [] (An empty array)
• {} (An empty object)
• function() {} (An empty function)

Falsy Values

A falsy value evaluates to false. If you place a falsy value inside an if statement, the block will not execute.

if (0) {
  // This will never execute
  console.log("0 is falsy");
}

There are exactly 6 common falsy values in JavaScript. It is highly recommended to memorize this list:

• false
• 0 (The number zero)
• "" (An empty string)
• null
• undefined
• NaN (Not a Number)

Practical Example

Because numbers other than 0 are truthy, you can use numeric variables directly in if statements to check if a user has sufficient quantity of an item. However, you must be careful with negative numbers, as they are also truthy!

// A bug: -2 is truthy, so the condition evaluates to true!
const userCredits = -2;

// To fix this, you should explicitly check > 0 rather than relying on truthiness alone
if (userCredits > 0) {
  console.log("Processing action...");
} else {
  console.log("Not enough credits.");
}