require-no-fallthrough-cases-in-switch

Require "noFallthroughCasesInSwitch": true in compilerOptions so that TypeScript reports an error for switch cases that fall through without an explicit terminator.

Targeted pattern scope

The compilerOptions.noFallthroughCasesInSwitch field in any tsconfig*.json file.

What this rule reports

This rule reports when compilerOptions.noFallthroughCasesInSwitch is absent or explicitly set to false.

Why this rule exists

switch fall-through is one of the most common sources of latent bugs in JavaScript and TypeScript. When a case block is not terminated by break, return, or throw, execution continues into the next case body, even if the next case condition does not match:

switch (action) {
    case "increment":
        count++;
    // ← missing break — falls through to "decrement"!
    case "decrement":
        count--;
        break;
}

This is almost always unintentional. Intentional fall-through (sharing a code path between two case labels) can still be expressed by placing the labels consecutively with no code between them:

switch (action) {
    case "increment":
    case "increase": // explicit shared case — TypeScript allows this
        count++;
        break;
}

noFallthroughCasesInSwitch: true makes TypeScript report an error on the first pattern above while allowing the second.

The auto-fixer adds "noFallthroughCasesInSwitch": true to compilerOptions.

❌ Incorrect

{
    "compilerOptions": {
        "target": "ES2022",
        "module": "NodeNext"
    }
}

noFallthroughCasesInSwitch is absent; fall-through cases go unreported.

{
    "compilerOptions": {
        "noFallthroughCasesInSwitch": false
    }
}

Explicitly disabled.

✅ Correct

{
    "compilerOptions": {
        "noFallthroughCasesInSwitch": true
    }
}

All non-empty switch cases must explicitly terminate.

When not to use it

Disable this rule in projects that intentionally rely on fall-through as a control-flow pattern, or that use a linting rule (such as ESLint's built-in no-fallthrough) to enforce this at the source level instead.

Package documentation

Rule catalog ID: R032

Targeted pattern scope​

What this rule reports​

Why this rule exists​

❌ Incorrect​

✅ Correct​

When not to use it​

Package documentation​

Further reading​