Truthy and Falsy

A "truthy" value is a value that is considered true when encountered in a Boolean context. In JavaScript, you don't need to explicitly convert a value to a Boolean before using it in a conditional:

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

A "falsy" value works the same way, but for values that evaluate to false:

if (!0) {
  console.log("0 is falsy");
}
if (!null) {
  console.log("null is falsy");
}
if (!undefined) {
  console.log("undefined is falsy");
}

Common truthy values include:

• true
• 42 (any number that isn't 0)
• "hello" (any non-empty string)
• [] (an empty array)
• {} (an empty object)
• function() {} (an empty function)

Common falsy values include:

• false
• 0
• "" (an empty string)
• null
• undefined
• NaN (Not a Number)