Operators and comparisons

Last reviewed May 28, 2026 Content v20260528

Track mode

client_javascript

Means

In-browser JS

Reading

~1 min

Level

beginner

This lesson

This lesson teaches Operators and comparisons—the ideas, syntax, and habits you need before moving on in JavaScript.

Without a solid grasp of Operators and comparisons, you will repeat mistakes in JavaScript exercises and on real pages or scripts.

You will apply Operators and comparisons in contexts like: Browsers, Node.js services, edge workers, and tooling ecosystems (bundlers, test runners).

Run JavaScript in the in-browser sandbox, use the terminal output panel, and verify with MCQs.

When the previous lesson's MCQs feel easy and you can explain Operators and comparisons in your own words.

Arithmetic (+ - * / %), logical (&& || !), and comparison operators drive control flow.

Truthy and falsy

Falsy: false, 0, '', null, undefined, NaN. Everything else is truthy—including '0' and [].

?? returns right side only when left is null or undefined—unlike || which treats 0 as missing.

Q: || vs ??
A: || treats 0 and '' as falsy; ?? only null/undefined.
Q: Short-circuit &&?
A: Stops evaluating when left is falsy—used for guards.

Pitfall: == coerces types—prefer ===.

Playground

Runs in your browser in a sandboxed frame. Backend runners appear when this track’s profile allows them.

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