switch

In JavaScript, the switch keyword starts a statement that compares one value against a list of case clauses and runs the code from the first clause that matches. An optional default clause runs when no case matches. Matching uses strict equality (===), so "1" doesn’t match 1 and NaN never matches anything.

Once a clause matches, execution runs to the end of the switch body unless a break, return, or throw leaves it first. Running on into the next clause is called fall-through.

The whole body is one block scope, so two clauses can’t both declare the same let or const name, and a using declaration directly inside a clause is a SyntaxError. Braces around a clause’s statements give them their own scope. For two or three branches, if and else are the common alternative.

JavaScript switch Keyword Syntax

A switch statement has the following form:

JavaScript Syntax 
switch (<expression>) {
  case <value1>:
    [<statements>]
  [case <value2>:
    [<statements>]]
  [default:
    [<statements>]]
}

The body allows at most one default clause, in any position.

JavaScript switch Keyword Examples

A switch statement maps HTTP status codes to messages, with one case that falls through:

JavaScript 
> function describeStatus(code) {
…   switch (code) {
…     case 200:
…       return "OK";
…     case 301:
…     case 302:
…       return "Redirect";
…     case 404:
…       return "Not Found";
…     default:
…       return "Unknown";
…   }
… }
undefined

> describeStatus(302)
'Redirect'

> describeStatus("404")
'Unknown'

The empty case 301: clause falls through to case 302:, so both codes share a result. The string "404" isn’t strictly equal to 404, so it reaches default.

Without a break, a matching clause keeps running into the clauses below it:

JavaScript 
> switch ("small") {
…   case "small":
…     console.log("Fits a small box");
…   case "medium":
…     console.log("Fits a medium box");
…     break;
…   case "large":
…     console.log("Fits a large box");
… }
Fits a small box
Fits a medium box
undefined

The break in the "medium" clause stops execution before "large".

JavaScript switch Keyword Use Cases

  • Choosing a branch from one value with several known options
  • Mapping status codes, commands, or action types to results
  • Grouping values that share a branch by stacking empty case clauses
  • Handling each kind of message in a reducer or event handler

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By Leodanis Pozo Ramos • Updated Nov. 4, 2026
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