Simple JavaScript Sandbox

examples.ts

const parser = Sandbox.compile('a + b');
const result = parser({ a: 1, b: 2 });

// ---

const parser = Sandbox.compile('a + b + alert', { throwOnUndefined: true });
const result = parser({ a: 1, b: 2 });

sandbox.ts

interface SandboxOptions {
  throwOnUndefined?: boolean;
}

class Sandbox {
  public static cache = new WeakMap();
  
  private constructor() {

  }

  public static compile(expression: string, options: SandboxOptions = {}) {
    return (context: any) => {
      let _context = Sandbox.cache.get(context);
      if (!_context) {
        _context = new Proxy(
          context, 
          {
            get: (target, p) => {
              if (p === Symbol.unscopables) {
                return undefined;
              }
              const value = target[p];
              if (options.throwOnUndefined && value === undefined) {
                throw new ReferenceError(`${ p.toString() } is not defined`);
              }
              return value;
            },
            has: () => true,
          },
        );
        Sandbox.cache.set(context, _context);
      }
      return (new Function('context', `with(context) { return (${ expression }) }`))(_context)
    };
  }

}