typescript/explicit-function-return-type Restriction ​
What it does ​
This rule enforces that functions have an explicit return type annotation.
Why is this bad? ​
Explicit return types make it clearer what type is returned by a function. Making the type returned by a function obvious allows the reader to infer what the function does and how it can be used from a quick glance.
Another benefit of explicit return types is the potential for a speed up of type checking in large codebases with many large functions.
Examples ​
Examples of incorrect code for this rule:
ts
// Should indicate that no value is returned (void)
function test() {
return
}
// Should indicate that a number is returned
var fn = function () {
return 1
}
// Should indicate that a string is returned
var arrowFn = () => 'test'
class Test {
// Should indicate that no value is returned (void)
method() {
return
}
}Examples of correct code for this rule:
ts
// No return value should be expected (void)
function test(): void {
return
}
// A return value of type number
var fn = function (): number {
return 1
}
// A return value of type string
var arrowFn = (): string => 'test'
class Test {
// No return value should be expected (void)
method(): void {
return
}
}Configuration ​
This rule accepts a configuration object with the following properties:
allowConciseArrowFunctionExpressionsStartingWithVoid ​
type: boolean
default: false
Whether to allow concise arrow functions that start with the void keyword.
allowDirectConstAssertionInArrowFunctions ​
type: boolean
default: true
Whether to allow arrow functions that use as const assertion on their return value.
allowExpressions ​
type: boolean
default: false
Whether to allow expressions as function return types. When true, allows functions that immediately return an expression without a return type annotation.
allowFunctionsWithoutTypeParameters ​
type: boolean
default: false
Whether to allow functions that do not have generic type parameters.
allowHigherOrderFunctions ​
type: boolean
default: true
Whether to allow higher-order functions (functions that return another function) without return type annotations.
allowIIFEs ​
type: boolean
default: false
Whether to allow immediately invoked function expressions (IIFEs) without return type annotations.
allowTypedFunctionExpressions ​
type: boolean
default: true
Whether to allow typed function expressions. When true, allows function expressions that are assigned to a typed variable or parameter.
allowedNames ​
type: string[]
default: []
Array of function names that are exempt from requiring return type annotations.
How to use ​
To enable this rule using the config file or in the CLI, you can use:
json
{
"rules": {
"typescript/explicit-function-return-type": "error"
}
}bash
oxlint --deny typescript/explicit-function-return-type