Combine values with operators and expressions

One idea at a time

An operator performs an operation on values called operands. In 4 + 2, + is the operator and 4 and 2 are its operands. The whole expression evaluates to 6. Multiplication runs before addition: 2 + 3 * 4 is 14, while (2 + 3) * 4 is 20. This priority is called precedence. A statement can use an expression, for example assigning its result or logging it. Parentheses group calculations when you want their order to be obvious.

Numbers support addition, subtraction, multiplication, division, and remainder. The same + operator also joins strings. If a string participates in addition, JavaScript may join text instead of adding numbers. Prefer explicit conversion when input is supposed to be numeric. Comparison expressions produce booleans that conditions can use in the next lesson.

What to remember first

Walk through an example

const price = 10;
const quantity = 3;
console.log(price * quantity);
console.log(7 % 2);
console.log(3 === "3");
console.log(Number("3") === 3);

Multiplication produces 30, remainder produces 1, and strict equality rejects the mismatched types. Explicit conversion makes the final comparison true. It does not change the original string; Number returns a new value. Division such as 10 / 3 produces a repeating decimal approximation, not exactly 3.33.

See it happen: try a small change

console.log(2 + 3);
console.log("2" + 3);
console.log(Number("2") + 3);

Look a little closer

Values also have truthiness when used as conditions. false, zero, an empty string, null, undefined, and NaN are common falsy values. A nonempty string such as false written in quotes is truthy. The || fallback therefore replaces zero too; the ?? operator only replaces null or undefined. Compare the fallback variant before choosing a default for a real count.

A template literal uses backticks instead of quotes. Inside it, ${expression} inserts a calculated value into text. For example, `Total: ${price * quantity}` creates a readable label. This is another way to combine text and values without a long chain of + operations; it does not update automatically when variables change later.

Try it in your own project

Use the existing linked script and Console. Run the numeric calculation, then compare a quoted quantity with a number. Replace the quantity with zero and check that the total is zero. Save and reload for each case.

The interactive preview runs in its own isolated document. Its Output panel mirrors console.log messages; it is not a full DevTools console. Choosing another version or resetting starts a fresh example and does not edit your local files. Read any simulation label: storage and request demonstrations explain their offline substitutes, while the written local examples use the real browser APIs.

A common wrong turn

Do not use = when you mean ===. Also avoid assuming a numeric-looking input is already a number. Check the value and type before calculating, and keep the meaningful number 0 when choosing a default. Parentheses improve clarity even when operator precedence would already give the intended result.

Go to the source

• MDN: Combine values with operators and expressions ↗

Examples are authored for Tuklas and checked with code and reference documentation. This is not a claim of independent human review. Suggest a correction.