Type Coercion (== vs ===, truthy & falsy)

JavaScript has a habit of quietly converting values between types. It's why "5" + 1 is "51" but "5" - 1 is 4 . These "WAT" moments confuse beginners, but once you understand the rules they become completely predictable.

Learn Type Coercion (== vs ===, truthy & falsy) in our free JavaScript course — a beginner-friendly interactive lesson with runnable examples, a practice…

Part of the free JavaScript course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

This lesson demystifies coercion, the falsy values, and the single habit that prevents most equality bugs: always use === .

🌐 Real-World Analogy: Coercion is like an over-eager travel agent who auto-converts currency:

Implicit coercion happens automatically inside operations. Explicit coercion is when you convert on purpose. The same conversion, two ways:

+ means addition and string concatenation. If either operand is a string, JavaScript concatenates; otherwise it adds. Every other math operator ( - * / % ) always coerces to numbers.

(The blank line is the empty string from [] + [] .)

Any value used in a boolean context (an if , && , ! ) is coerced to true or false. There are exactly eight falsy values — everything else is truthy.

=== (strict) compares value and type with no conversion. == (loose) coerces first, which leads to genuinely bizarre results. The lesson: use === .

Look at the contradiction: 0 == "" and 0 == "0" are both true, yet "" == "0" is false. Loose equality is not transitive — another reason to avoid it.

When you control the conversion, your code is clear and bug-resistant. Here are the idiomatic patterns:

These lines should safely turn a form value into a number, defaulting to 0 for invalid input, and report whether it's positive. They are scrambled — reorder them.

Why: the raw text (B) must exist before conversion (D). Number trims the surrounding spaces and yields 42 . The guard (A) replaces NaN with 0 so bad input can't poison later math. Only then can the result be reported (C). Note the final + here is string concatenation because the left side starts with a number followed by a string literal.

123 — evaluated left to right: 1 + "2" concatenates to "12" (because one side is a string), then "12" + 3 concatenates to "123" .

Only A prints. The string "0" is non-empty, so it's truthy. The number 0 is one of the eight falsy values, so the second if is skipped.

true false — loose == has a special rule making null and undefined equal to each other. Strict === checks type too, and they are different types, so it's false .

Up next: a Checkpoint that combines iterators, strings, numbers, loops and conditionals into one build! 🏁

Practice quiz

• Browse all free courses
• Cheat sheets & quizzes
• Coding dictionary