TypeScript - Get a Lambda expression as a string

One of the things I really like about C# is the ability to convert a lambda into a string. It's useful for doing all kinds of things, especially when you are calling a 3rd party library's method that expects a string identifying a member of an object.

I saw this was lacking in TypeScript, which was a pain because I wanted to make various parts of my Angular application more compile-time resilient to changes in the server's API model.

Using the following code it is possible to take a call like this

someObject.doSomething<Person>(x => x.firstName)

From there we can get the name of the property referenced in the lamba expression. In fact it will return the entire path after the "x."

abstract class Expression {
  private static readonly pathExtractor = new RegExp('return (.*);');

  public static path<T>(name: (t: T) => any) {
    const match = Expression.pathExtractor.exec(name + '');
    if (match == null) {
      throw new Error('The function does not contain a statement matching \'return variableName;\'');
    }
    return match[1].split('.').splice(1).join('.');
  }
}

Example

The following example will show the string 'country.code'

interface Address {
    line1: string;
    country: {
        code: string;
        name: string;
    }
}

const result = Expression.path<address>(x => x.country.code);
alert('Result is ' + result);