Lazy / Memoize decorator for TypeScript's getter

memoize.ts

export function memoize(target: any, prop: string, descriptor: PropertyDescriptor)
{
    let original = descriptor.get;

    descriptor.get = function (...args: any[])
    {
        const privateProp = `__memoized_${prop}`;

        if (!this.hasOwnProperty(privateProp)) {
            Object.defineProperty(this, privateProp, {
                configurable: false,
                enumerable: false,
                writable: false,
                value: original.apply(this, args)
            });
        }

        return this[privateProp];
    };
}

usage.ts

export class Foo{
  @memoize get bar()
  {
    return 1 + 1; // will be calculated once and then cached
  }
}

Nice, thanks for posting! I also made a decorator to memoize an accessor get but I used a closure to store the memoized value:

export function memoize(_target: any,  _prop: string,  descriptor: PropertyDescriptor): void {
  let original = descriptor.get;
  let cachedValue: any; // Store value in closure scope.

  descriptor.get = function () {
    if (!cachedValue) {
      cachedValue = original.call(this);
      original = undefined; // Drop reference to original function to allow it to be garbage collected.
    }
    return cachedValue;
  };
}