“Truthy and Falsy: The Logic You Didn’t Know You Were Using”

Hello everyone!
Today we are going to see about the topic of truthy and falsy
Introduction: Everyday Logic in Code

• Start with a relatable hook (example: "Have you ever seen JavaScript behave strangely in an if condition?")
• Introduce the idea that JavaScript doesn’t just use true and false—it interprets many values in a boolean way.
• Set the tone that this blog will uncover this “hidden logic”.

What Does ‘Truthy’ and ‘Falsy’ Mean?

• Define “truthy” = values that behave like true
• Define “falsy” = values that behave like false
• Mention it’s part of type coercion in JavaScript

The 7 Falsy Values in JavaScript

List and explain briefly:

1. false
2. 0
3. "" (empty string)
4. null
5. undefined
6. NaN
7. document.all (rare case)

Example:

js
if (0) {
console.log("This won't run, because 0 is falsy");
}

Examples of Truthy Values

• Almost everything else is truthy: non-empty strings, arrays, objects, numbers other than 0
• Show some examples:

js
if ("hello") console.log("Truthy string");
if ([]) console.log("Truthy empty array");

Why This Matters in Real Projects

• Show where truthy/falsy values sneak in:

  • Conditionals
  • Logical operators ||, &&
  • Ternary operators
  • Default value fallbacks

Example:

js
let username = userInput || "Guest";

Common Mistakes Developers Make

• Using == instead of ===
• Assuming empty arrays or objects are falsy (they’re truthy!)
• Forgetting NaN is falsy

How to Check If a Value is Truthy or Falsy

• Use Boolean() or double !!: js console.log(Boolean("hello")); // true console.log(Boolean("")); // false

Conclusion: Logic You Now Understand

• Wrap up with how knowing truthy/falsy can help avoid bugs
• Encourage testing values and using strict equality when needed