When it comes to making functions in typescript, the language can often infer the return type automatically. Take for instance this basic function:
function calculateProduct(x: number, y: number) {
return x * y;
}
However, there are scenarios where declaring the return type is necessary. This usually occurs when another function call within the main function is returning any, preventing TypeScript from making a proper inference.
function calculateProduct(x: number, y: number) {
return x * y || fetchAnyValue();
}
In such cases, it's best practice to explicitly type the return value if you know that fetchAnyValue() will return a number.
function calculateProduct(x: number, y: number): number {
return x * y || fetchAnyValue();
}
Another approach could be to simply type the fetchAnyValue() function itself. By doing so, TypeScript can properly infer the return type without the need for explicit declarations within individual functions. The question then arises - when should one use explicit return types? It seems that they are most useful in situations involving uncertain return values or complex function calls.