true, false, truthy and falsy.
✍️ 3 exercises + code challenge in this lessonA boolean is either true or false. Comparisons produce booleans.
In conditions, every value acts as true or false. These values are falsy:
false, 0, "" (empty string), null, undefined, NaN
Everything else is truthy, including "0", [] and {}.
Mastering JavaScript Booleans & Comparisons helps you write clean and reliable JavaScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
<pre id="out"></pre>
<script>
const log = (...a) => document.getElementById("out").textContent += a.join(" ") + "\n";
log("10 > 9:", 10 > 9);
log("'apple' < 'banana':", "apple" < "banana");
const values = [0, 1, "", "hello", null, undefined, NaN, [], {}];
for (const v of values) {
log(JSON.stringify(v) ?? String(v), "is", v ? "truthy" : "falsy");
}
log(Boolean("0"));
</script>Check what you learned in “JavaScript Booleans & Comparisons”.
Convert any value to a boolean.
("hello") // true
Which of these values is falsy?
Log whether 10 is greater than 9 (it should print true).
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