JavaScript Operators

An operator is a small symbol that does something to values: + adds, * multiplies, === checks whether two things are equal. Operators are the verbs of JavaScript — variables hold the nouns, and operators are what you do with them.

Diagram — see how it fits together

There are four groups you need: arithmetic operators for maths, assignment operators for storing values, comparison operators for asking questions, and logical operators for combining questions. Together they cover almost everything a beginner program does.

Arithmetic — doing the maths

The arithmetic operators are + add, - subtract, * multiply, / divide, % remainder, and ** power. The remainder operator % is the one beginners meet last and use most: 10 % 3 is 1, because 10 divided by 3 leaves 1 over. It is how programs check whether a number is even (n % 2 === 0) or split items into groups.

let total = 4 * 15;      // 60
let change = 100 - 60;   // 40
let isEven = 10 % 2 === 0; // true

Assignment — storing and updating

The plain assignment = stores a value. The shortcuts combine an operation with storing: += adds and stores, -= subtracts and stores, *= and /= do the same for multiply and divide. total += 10 means exactly the same as total = total + 10, but shorter. Two more shortcuts: ++ adds one, -- subtracts one.

let score = 50;
score += 10; // score is now 60
score++;     // score is now 61

Comparison — asking yes/no questions

Comparison operators answer with true or false: === strictly equal, !== strictly not equal, > greater than, < less than, >= and <=. Always use === and !==, not == and !=. The double-equals versions convert types before comparing, so "10" == 10 is true — a surprise nobody wants. Triple equals compares value and type, so "10" === 10 is false, which is honest.

let marks = 75;
marks >= 33;  // true — the student passed
marks === 75; // true
"75" === 75;  // false — a string is not a number

Logical — combining questions

Logical operators combine true/false answers: && means AND (both must be true), || means OR (at least one must be true), ! means NOT (flips true to false). A scholarship might need marks above 80 and attendance above 90% — that is one &&. A discount might apply to students or teachers — that is one ||.

let passed = marks >= 33;
let distinction = marks >= 75;
passed && distinction; // true only if both are true

Common mistakes

• Using == instead of === — the loose version converts types and hides real differences between strings and numbers.
• Using = inside a condition — it stores a value instead of comparing, and the condition is always true.
• Writing & or | (single) when you mean && or || (double) — the single versions are bit operators, a different thing entirely.
• Forgetting that + also joins text — "5" + 3 is "53", not 8, because + with a string means "join".

Remember

• Arithmetic: + - * / % **. The remainder % checks even numbers and groups.
• Assignment: = += -= *= /=, plus ++ and --.
• Comparison: === !== > < >= <=. Always use the triple versions.
• Logical: && AND, || OR, ! NOT.

Example explained

• Number(document.getElementById("marks").value) — reads the marks the visitor typed and turns the text into a number, so the maths works properly.
• marks >= 33 — a comparison that answers true or false: did the student reach the pass marks?
• marks >= 75 — a second comparison for distinction. Both answers are stored in variables, not thrown away.
• passed && distinction — the AND operator: true only when the student both passed and scored a distinction.
• if ... else — picks one of two messages based on the answers. You will learn the full if statement in the Conditions lesson; here, just notice how the operators feed it true or false.