JavaScript Truthy/Falsy and Logical Operator Cheatsheet

The Six Falsy Values in JavaScript

1. undefined
2. null
3. NaN
4. 0
5. ""
6. false

Everything else is truthy. (i.e. [], {}, "false")

&& and || Return values

A good rule of thumb for remembering the return values of these operators.

JavaScript will want to do the least amount of work to get its return value.

&&: will first try to return the first falsy value. If none found, it will return the last truthy value.

||: will first try to return the first truthy value. If none found, it will return the last falsy value.

const falsy1 = null;
const falsy2 = NaN;
const truthy1 = 'c';
const truthy2 = 'd';
// both are truthy
console.log(truthy1 && truthy2); // truthy2
console.log(truthy1 || truthy2); // truthy1
// both are falsy
console.log(falsy1 && falsy2); // falsy1
console.log(falsy1 || falsy2); // falsy2
// 1st truthy, 2nd falsy
console.log(truthy1 && falsy1); // falsy1
console.log(truthy1 || falsy1); // truthy1
// 1st falsy, 2nd truthy
console.log(falsy1 && truthy1); // falsy1
console.log(falsy1 || truthy1); // truthy1