Safe way to extract property names

In TS 2.1 the keyof keyword was introduced which made this possible:

function propertyOf<TObj>(name: keyof TObj) {
    return name;
}

or

function propertiesOf<TObj>(_obj: (TObj | undefined) = undefined) {
    return function result<T extends keyof TObj>(name: T) {
        return name;
    }
}

or using Proxy

export function proxiedPropertiesOf<TObj>(obj?: TObj) {
    return new Proxy({}, {
        get: (_, prop) => prop,
        set: () => {
        throw Error('Set not supported');
        },
    }) as {
        [P in keyof TObj]?: P;
    };
}

These can then be used like this:

propertyOf<MyInterface>("myProperty");

or

const myInterfaceProperties = propertiesOf<MyInterface>();
myInterfaceProperties("myProperty");

or

const myInterfaceProperties = propertiesOf(myObj);
myInterfaceProperties("myProperty");

or

const myInterfaceProperties = proxiedPropertiesOf<MyInterface>();
myInterfaceProperties.myProperty;

or

const myInterfaceProperties = proxiedPropertiesOf(myObj);
myInterfaceProperties.myProperty;

Right now there's not really a great way of doing this, but there are currently some open suggestions on github (See #1579, #394, and #1003).

What you can do, is what's shown in this answer—wrap referencing the property in a function, convert the function to a string, then extract the property name out of the string.

Here's a function to do that:

function getPropertyName(propertyFunction: Function) {
    return /\.([^\.;]+);?\s*\}$/.exec(propertyFunction.toString())[1];
}

Then use it like so:

// nameProperty will hold "name"
const nameProperty = getPropertyName(() => this.state.name);

This might not work depending on how the code is minified so just watch out for that.

Update

It's safer to do this at compile time. I wrote ts-nameof so this is possible:

nameof<User>(s => s.name);

Compiles to:

"name";