ReactiveVariable.js

class ReactiveVariable {
    constructor(val, handle) {
      if(typeof handle === 'function') {
        this.Value = val;
        this.Handle = handle;
      } else console.error('ReactiveVariable needs a handler function after the value');
      return this.Value;
    }
    set(val) {
      if(this.Value !== val) {
        this.Oldval = this.Value;
        this.Value = val;
        this.Handle(this.Oldval,val);
      }
      return this.Value;
    }
    Reset(handle) {
      if(typeof handle === 'function') {
        this.Handle = handle;
      } else console.error('ReactiveVariable.Reset only takes a function');
    }
  }

Tiny Data Bind System that uses handlers and manual setting