compiler-checks-for-unused-params-and-variables.md

Compiler Checks For Unused Params And Variables

There are a number of linter-esque checks that you can tell the TypeScript compiler to make when it is checking your code. There are two that prevent values from going unused: one for parameters and the other for variables.

The noUnusedLocals config, which defaults to false, can be set to true. This will cause the compiler to fail if a locally declared variable goes unused.

function printItem(item: any, index: number) {
  const indexedItem = `${index}: ${item}`;
  //    ^^^ 'indexedItem' is declared but its value is never read.

  console.log(item);
}

The noUnusedParameters config, which also defaults to false, can be set to true. This will cause the compiler to fail if a function param goes unused.

Fixing the previous error could then result in this one.

function printItem(item: any, index: number) {
  //                          ^^^
  // 'index' is declared but its value is never read.

  console.log(item);
}

Here is what the tsconfig.json would look like:

{
  "compilerOptions": {
    "noUnusedLocals": true,
    "noUnusedParameters": true,
  }
}