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if-else

if-else

Introduction

The if statement executes a block of code if a condition is truthy. else if and else provide alternative branches.

Syntax

if (condition) {
  // runs if condition is truthy
} else if (otherCondition) {
  // runs if first condition is falsy and otherCondition is truthy
} else {
  // runs if all conditions are falsy
}

Visual Explanation

flowchart TD
    Start["Start"]
    Cond{"age >= 18?"}
    Yes["You are an adult"]
    No["You are a minor"]

    Start --> Cond
    Cond -->|Yes| Yes
    Cond -->|No| No

Examples

const age = 20;

if (age >= 18) {
  console.log('You can vote');
} else if (age >= 16) {
  console.log('You can drive');
} else {
  console.log('Too young');
}

Truthiness in Conditions

if ('hello') { }     // runs — truthy
if (0) { }            // doesn't run — falsy
if (null) { }         // doesn't run — falsy
if ([]) { }           // runs — truthy (empty array)
if ({}) { }           // runs — truthy (empty object)

Best Practices

Always use === for comparisons (not ==)
Prefer switch for many conditions on the same value
Use guard clauses to avoid deep nesting

Further Reading

MDN: if-else