Ineffective parameter type¶
ID: js/ineffective-parameter-type Kind: problem Security severity: Severity: warning Precision: high Tags: - quality - reliability - correctness - typescript Query suites: - javascript-code-quality.qls - javascript-security-and-quality.qls
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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.
Recommendation¶
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.
Example¶
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 items.map(callback).join(", ") }
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 items.map(callback).join(", ") }
Untyped parameters are illegal when compiling with the TypeScript flag --noImplicitAny.