Learn how to make TypeScript catch missing switch cases at compile time using the exhaustive switch pattern with the never type.

TypeScript.TV

TypeScript's exhaustive switch pattern uses the `never` type to catch missing switch cases at compile time. By adding a default case that assigns the switch variable to a `never` type, the compiler verifies all enum or union type values are handled. When a new case is added but not handled, TypeScript throws a compile error, preventing silent bugs from reaching production. This pattern works with enums and discriminated unions, shifting error detection from runtime to compile time and proving especially valuable in large codebases where types evolve over time.

Never Miss a Switch Case Again

The Problem with Regular Switch Statements

Set <code>noImplicitReturns</code> to true and you don’t have to do this. Then the following will work out of the box:
<pre><code>enum EnumType {
 foo,
 bar,
 baz
}

const exhaustiveEnumCase = (v: EnumType) =&gt; {
 switch (v) {
 case EnumType.foo:
 return 42;
 case EnumType.bar:
 return &quot;six-seven&quot;;
 }
};
</code></pre>
Ts will let you know <code>Not all code paths return a value.</code> if you ever update the enum. Works for union types, object keys, etc.

In the article <code>enum</code>s are used, which are considered harmful nowadays. I wonder what it would look like with <code>as const</code> instead.