JavaScript Comparison Operators

A comparison operator compares two values and returns a boolean.

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const age = 18;
console.log(age > 17);   // → true
console.log(age >= 18);  // → true
console.log(age < 18);   // → false
console.log(age === 18); // → true
console.log(age !== 18); // → false

Comparing strings

Strings are compared character by character using their Unicode order. Capital letters come before lowercase ones.

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console.log("apple" < "banana"); // → true
console.log("a" < "B");          // → false
console.log("Zebra" < "apple");  // → true

For sorting words for people, use localeCompare() instead, which follows language rules: "a".localeCompare("B").

Comparing different types

When the types differ, the loose operators try to convert them first. That is where surprises start.

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console.log("10" > 9);   // → true  ("10" becomes the number 10)
console.log("10" > "9"); // → false (both strings: "1" comes before "9")

The same two values give different answers depending on their type. Convert to numbers first whenever you mean numeric comparison.

NaN is never equal to anything

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console.log(NaN === NaN);        // → false
console.log(Number.isNaN(NaN));  // → true

To check for NaN, use Number.isNaN(), see Numbers.

Equality has its own lesson, because the difference between == and === is one of the most asked beginner questions: Strict vs Loose Equality.