if...else and switch

Syntax

if (condition) { } else if (condition) { } else { }
switch (value) { case x: break; default: }

Examples

function getGrade(score) {
  if (score >= 90) {
    return "A";
  } else if (score >= 80) {
    return "B";
  } else if (score >= 70) {
    return "C";
  } else {
    return "F";
  }
}

console.log(getGrade(85)); // "B"

function getDayName(day) {
  switch (day) {
    case 0:
      return "Sunday";
    case 1:
      return "Monday";
    case 2:
      return "Tuesday";
    default:
      return "Unknown";
  }
}

console.log(getDayName(1)); // "Monday"

// Fall-through: cases without break share the same code
function isWeekend(day) {
  switch (day) {
    case 0:
    case 6:
      return true;
    default:
      return false;
  }
}

Best practices

• Use switch when comparing one value against many discrete options - it is more readable than a long if/else if chain in that case
• Never forget the break statement in each switch case, or execution will fall through into the next case unintentionally
• Always include a default case in a switch to handle unexpected values
• For simple boolean conditions, prefer if/else or a ternary over switch

At a glance

Purpose

Application logic and interaction

File extension

.js · .mjs

Runs in

Browsers and JavaScript runtimes

Usually used with

HTML, CSS and Web APIs

Specifications & further reading

• ECMAScript specification

Related JavaScript documentation