A boolean is the simplest type of all. It has only two possible values: true and false. That's it. Yes or no. On or off. Light switch up or light switch down.
const isRaining = true;
const hasHomework = false;
console.log(isRaining);
console.log(hasHomework);It prints
true false
Notice there are no quotes. true is a boolean. "true" is a string containing four letters. Very different things!
Booleans are named after George Boole, a 19th-century mathematician who worked out the math of true-and-false logic long before computers existed.
You'll usually get booleans as the answer to a question, like "is 10 bigger than 5?":
console.log(10 > 5);
console.log(10 < 5);
console.log("hello".includes("ell"));It prints
true false true
Booleans might seem boring now, but they're the secret ingredient that lets programs make decisions. In Grade 4, you'll use them to write code like "if the password is correct, let them in; otherwise, show an error." They're kind of a big deal.