TypeScript - nameof operator equivalent

11/06/2017

Gérald Barré

Web
TypeScript
Web

A lot of JavaScript frameworks involve computation based on the property name of an object. So, you end with magic strings in your code. Magic strings are bad because it makes your code hard to refactor, you cannot find all references, etc. In C# 6, you can use the nameof operator. This is very useful. However, this is not possible in TypeScript yet. There are many issues asking to support this operator. In the meanwhile, you can create a function that simulates thenameof operator, at least for the most common case, using the keyof operator.

function nameof<T>(key: keyof T, instance?: T): keyof T {
    return key;
}

You can use the function using 2 ways:

function test(user: User) {
    nameof<User>("id"); // returns "id"
    nameof<User>("Id"); // Error
    nameof("id", user); // returns "id", without specifying the generic type
}

The nameof function is very cool because it checks the string is valid and it also provides autocompletion 😃