JavaScript

This page explains how if, else if, and else choose which code block runs.

Goal: branch safely based on conditions and make the order of checks easy to understand.

if...else

An if statement runs its block when its condition is truthy. If the condition is false, an optional else block can run instead.

const age = 20;

if (age >= 18) {
  console.log("Adult");
} else {
  console.log("Under 18");
}

Several cases with else if

const score = 82;

if (score >= 90) {
  console.log("A");
} else if (score >= 70) {
  console.log("B");
} else {
  console.log("C");
}

JavaScript checks the conditions from top to bottom and runs the first matching block. Once a block runs, the remaining branches are skipped.

Build clear conditions

Comparison operators such as ===, >, and <= produce Booleans. Logical operators such as &&, ||, and ! combine conditions.

const age = 20;
const hasTicket = true;

if (age >= 18 && hasTicket) {
  console.log("May enter");
}

Practical tips

• Use braces even for a one-line block; they make later edits safer.
• Prefer strict comparisons such as === when comparing values.
• Order overlapping ranges from the most specific or highest threshold to the fallback.
• Use switch when one value is compared against many fixed cases.

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