switch
======

The **`switch`** statement evaluates an expression, matching the expression's value against a series of `case` clauses, and executes statements after the first `case` clause with a matching value, until a `break` statement is encountered. The `default` clause of a `switch` statement will be jumped to if no `case` matches the expression's value.

Try it
------

Syntax
------


```js
switch (expression) {
  case caseExpression1:
    statements
  case caseExpression2:
    statements
  // …
  case caseExpressionN:
    statements
  default:
    statements
}
```


`expression`

An expression whose result is matched against each `case` clause.

`case caseExpressionN` Optional

A `case` clause used to match against `expression`. If the value of `expression` matches the value of any `caseExpressionN`, execution starts from the first statement after that `case` clause until either the end of the `switch` statement or the first encountered `break`.

`default` Optional

A `default` clause; if provided, this clause is executed if the value of `expression` doesn't match any of the `case` clauses. A `switch` statement can only have one `default` clause.

Description
-----------

A `switch` statement first evaluates its expression. It then looks for the first `case` clause whose expression evaluates to the same value as the result of the input expression (using the strict equality comparison) and transfers control to that clause, executing all statements following that clause.

The clause expressions are only evaluated when necessary — if a match is already found, subsequent `case` clause expressions will not be evaluated, even when they will be visited by fall-through.


```js
switch (undefined) {
  case console.log(1):
  case console.log(2):
}
// Only logs 1
```


If no matching `case` clause is found, the program looks for the optional `default` clause, and if found, transfers control to that clause, executing statements following that clause. If no `default` clause is found, the program continues execution at the statement following the end of `switch`. By convention, the `default` clause is the last clause, but it does not need to be so. A `switch` statement may only have one `default` clause; multiple `default` clauses will result in a `SyntaxError`.

### Breaking and fall-through

You can use the `break` statement within a `switch` statement's body to break out early, often when all statements between two `case` clauses have been executed. Execution will continue at the first statement following `switch`.

If `break` is omitted, execution will proceed to the next `case` clause, even to the `default` clause, regardless of whether the value of that clause's expression matches. This behavior is called "fall-through".


```js
const foo = 0;
switch (foo) {
  case -1:
    console.log("negative 1");
    break;
  case 0: // Value of foo matches this criteria; execution starts from here
    console.log(0);
  // Forgotten break! Execution falls through
  case 1: // no break statement in 'case 0:' so this case will run as well
    console.log(1);
    break; // Break encountered; will not continue into 'case 2:'
  case 2:
    console.log(2);
    break;
  default:
    console.log("default");
}
// Logs 0 and 1
```


In the appropriate context, other control-flow statements also have the effect of breaking out of the `switch` statement. For example, if the `switch` statement is contained in a function, then a `return` statement terminates the execution of the function body and therefore the `switch` statement. If the `switch` statement is contained in a loop, then a `continue` statement stops the `switch` statement and jumps to the next iteration of the loop.

### Lexical scoping

The `case` and `default` clauses are like labels: they indicate possible places that control flow may jump to. However, they don't create lexical scopes themselves (neither do they automatically break out — as demonstrated above). For example:


```js
const action = "say\_hello";
switch (action) {
  case "say\_hello":
    const message = "hello";
    console.log(message);
    break;
  case "say\_hi":
    const message = "hi";
    console.log(message);
    break;
  default:
    console.log("Empty action received.");
}
```


This example will output the error "Uncaught SyntaxError: Identifier 'message' has already been declared", because the first `const message = 'hello';` conflicts with the second `const message = 'hi';` declaration, even when they're within their own separate case clauses. Ultimately, this is due to both `const` declarations being within the same block scope created by the `switch` body.

To fix this, whenever you need to use `let` or `const` declarations in a `case` clause, wrap it in a block.


```js
const action = "say\_hello";
switch (action) {
  case "say\_hello": {
    const message = "hello";
    console.log(message);
    break;
  }
  case "say\_hi": {
    const message = "hi";
    console.log(message);
    break;
  }
  default: {
    console.log("Empty action received.");
  }
}
```


This code will now output `hello` in the console as it should, without any errors.

Examples
--------

### Using switch

In the following example, if `expr` evaluates to `Bananas`, the program matches the value with case `case 'Bananas'` and executes the associated statement. When `break` is encountered, the program breaks out of `switch` and executes the statement following `switch`. If `break` were omitted, the statement for the `case 'Cherries'` would also be executed.


```js
switch (expr) {
  case "Oranges":
    console.log("Oranges are $0.59 a pound.");
    break;
  case "Apples":
    console.log("Apples are $0.32 a pound.");
    break;
  case "Bananas":
    console.log("Bananas are $0.48 a pound.");
    break;
  case "Cherries":
    console.log("Cherries are $3.00 a pound.");
    break;
  case "Mangoes":
  case "Papayas":
    console.log("Mangoes and papayas are $2.79 a pound.");
    break;
  default:
    console.log(`Sorry, we are out of ${expr}.`);
}

console.log("Is there anything else you'd like?");
```

### Putting the default clause between two case clauses

If no match is found, execution will start from the `default` clause, and execute all statements after that.


```js
const foo = 5;
switch (foo) {
  case 2:
    console.log(2);
    break; // it encounters this break so will not continue into 'default:'
  default:
    console.log("default");
  // fall-through
  case 1:
    console.log("1");
}
```


It also works when you put `default` before all other `case` clauses.

### Taking advantage of fall-through

This method takes advantage of the fact that if there is no `break` below a `case` clause, execution will continue to the next `case` clause regardless if that `case` meets the criteria.

The following is an example of a single operation sequential `case` statement, where four different values perform exactly the same.


```js
const Animal = "Giraffe";
switch (Animal) {
  case "Cow":
  case "Giraffe":
  case "Dog":
  case "Pig":
    console.log("This animal is not extinct.");
    break;
  case "Dinosaur":
  default:
    console.log("This animal is extinct.");
}
```


The following is an example of a multiple-operation sequential `case` clause, where, depending on the provided integer, you can receive different output. This shows you that it will traverse in the order that you put the `case` clauses, and it does not have to be numerically sequential. In JavaScript, you can even mix in definitions of strings into these `case` statements as well.


```js
const foo = 1;
let output = "Output: ";
switch (foo) {
  case 0:
    output += "So ";
  case 1:
    output += "What ";
    output += "Is ";
  case 2:
    output += "Your ";
  case 3:
    output += "Name";
  case 4:
    output += "?";
    console.log(output);
    break;
  case 5:
    output += "!";
    console.log(output);
    break;
  default:
    console.log("Please pick a number from 0 to 5!");
}
```


The output from this example:

| Value | Log text |
| --- | --- |
| `foo` is `NaN` or not `1`, `2`, `3`, `4`, `5`, or `0` | Please pick a number from 0 to 5! |
| `0` | Output: So What Is Your Name? |
| `1` | Output: What Is Your Name? |
| `2` | Output: Your Name? |
| `3` | Output: Name? |
| `4` | Output: ? |
| `5` | Output: ! |

### An alternative to if...else chains

You may often find yourself doing a series of `if...else` matches.


```js
if ("fetch" in globalThis) {
  // Fetch a resource with fetch
} else if ("XMLHttpRequest" in globalThis) {
  // Fetch a resource with XMLHttpRequest
} else {
  // Fetch a resource with some custom AJAX logic
}
```


This pattern is not doing a sequence of `===` comparisons, but you can still convert it to a `switch` construct.


```js
switch (true) {
  case "fetch" in globalThis:
    // Fetch a resource with fetch
    break;
  case "XMLHttpRequest" in globalThis:
    // Fetch a resource with XMLHttpRequest
    break;
  default:
    // Fetch a resource with some custom AJAX logic
    break;
}
```


The `switch (true)` pattern as an alternative to `if...else` is especially useful if you want to utilize the fall-through behavior.


```js
switch (true) {
  case isSquare(shape):
    console.log("This shape is a square.");
  // Fall-through, since a square is a rectangle as well!
  case isRectangle(shape):
    console.log("This shape is a rectangle.");
  case isQuadrilateral(shape):
    console.log("This shape is a quadrilateral.");
    break;
  case isCircle(shape):
    console.log("This shape is a circle.");
    break;
}
```

Specifications
--------------

| Specification |
| --- |
| ECMAScript Language Specification # sec-switch-statement |

Browser compatibility
---------------------

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See also
--------

* `if...else`