ts-r
  • Error
  • Reported by the type checker

TS1345

An expression of type 'void' cannot be tested for truthiness.

The result of a `void` function is used as a condition. A `void` value is never meaningful to test; call the function and test something else.

What it means

An expression of type void is used in if, while, &&, ||, ! or a conditional expression. A function typed void returns nothing useful, so testing it is almost always a mistake, such as testing a callback's result instead of calling a predicate.

Example

index.ts
function save(): void {}

if (save()) {
  console.log("saved");
}
ts-r-check -p tsconfig.json --pretty false ts-r output
index.ts(3,5): error TS1345: An expression of type 'void' cannot be tested for truthiness.

Recorded by node scripts/verify-examples.mjs with ts-r built from commit 6deaf01. The example uses the default tsconfig: strict, target: es2022, module: esnext, moduleResolution: bundler.

How to fix

  • Call the function on its own line and test a real condition.
  • If the function does return a meaningful value, change its return type (for example to boolean).