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Core JavaScriptBeginner

Truthy and Falsy

JavaScript treats some values as truthy and some as falsy when evaluating conditions.

Conditions in JavaScript do not require actual booleans. Values like `0`, `""`, `null`, `undefined`, `NaN`, and `false` are falsy, while most other values are truthy. This matters in conditionals, logical operators, and default-value patterns.

Explanation

Conditions in JavaScript do not require actual booleans. Values like `0`, `""`, `null`, `undefined`, `NaN`, and `false` are falsy, while most other values are truthy. This matters in conditionals, logical operators, and default-value patterns.

Key Points

  • Falsy values are limited and should be memorized.
  • An empty array and empty object are still truthy.
  • Truthiness is about conditional evaluation, not the original data type.

Common Mistakes

  • Assuming `[]` or `{}` are falsy because they look empty.
  • Using `||` for defaults when `0` or an empty string is a valid value.
  • Confusing `null` and `undefined` checks with generic falsy checks.

Practice Workspace

truthy-falsy.js

Edit the code, run it in the browser, and inspect the console output below. Reset restores the original snippet for this page.

Editor

9 lines

Output

0 entries

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practice

Workspace Notes

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truthy-falsy.js
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Editor Actions

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Console0 entries

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Expected Output

empty string is falsy
empty array is truthy

Continue in Playground

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Related Concepts

Data Types

JavaScript has primitive and reference data types, and knowing the difference affects comparison, copying, and mutation.

Type Coercion

Type coercion is JavaScript converting one value type into another during operations or comparisons.

Equality

JavaScript has loose and strict equality, and they behave differently because loose equality allows coercion.

Practice Challenges

Keep valid falsy values

7 min

Use nullish coalescing so valid values like `0` are not replaced by defaults.