CodeQL documentation

Ineffective parameter type

ID: js/ineffective-parameter-type
Kind: problem
Severity: warning
Precision: high
   - correctness
   - typescript
Query suites:
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

In TypeScript, the parameters of a function signature must have a name and may optionally have a type. A common mistake is to try to omit the name. This means the type is instead seen as the name. As a result, the parameter type will default to any since no type was given.

Parameter names in function signatures are only relevant for documentation purposes but cannot be omitted.


Give both a name and type to the parameter, as it cannot be given a type without having a name. Alternatively, if the parameter is intentionally untyped, change its name so it does not coincide with a type name.


In the following example, the callback parameter is written as (T) => string, which actually means (T: any) => string and is not useful for type checking or code completion.

function join<T>(items: T[], callback: (T) => string) {
  return", ")

Amend this by changing the callback type to (item: T) => string. The parameter name item is only relevant for documentation purposes, but a name is required regardless.

function join<T>(items: T[], callback: (item: T) => string) {
  return", ")

Untyped parameters are illegal when compiling with the TypeScript flag --noImplicitAny.