Builder Pattern example code

builderPattern.ts

type IBuilder<T> = {
  [k in keyof T]: (arg: T[k]) => IBuilder<T>
} & { build(): T }

function proxyBuilder<T>(): IBuilder<T> {
  var built: any = {};
  var builder = new Proxy({}, {
    get: function(target, prop, receiver) {
      if (prop === 'build') return () => built;
      return (x: any): any => {
        (built[prop] = x);
        return builder;
      }
    }
  });
  return builder as any;
}

function keyBuilder<T>(allKeys: (keyof T)[]): IBuilder<T> {
  var built: any = {};
  var builder: any = { build: () => built };
  allKeys.forEach(k => {
    builder[k] = function(v: any) {
      built[k] = v;
      return builder;
    }
  });
  return builder as any;
}

////

interface IPoint {
  x: number;
  y: number;
  z?: number;
};

var point1 = proxyBuilder<IPoint>().x(1).y(2).build();
var point2 = keyBuilder<IPoint>(['x', 'y', 'z']).x(1).y(2).build();