typescript/explicit-function-return-type Restriction

What it does

This rule enforces that functions do have an explicit return type annotation.

Why is this bad?

Explicit return types do make it visually more clear what type is returned by a function. They can also speed up TypeScript type checking performance in large codebases with many large functions.

Example

Examples of incorrect code for this rule:

// 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:

// 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;
  }
}

References

• Rule Source