Small Observable function for data-binding and stuff using Proxies or Object.observe if Proxies are unavailable.

Observable.js

"use strict";
((doc,root) => {
      
      let isArraylike = o => typeof o['length'] !== "undefined", 
      isFunc = o => typeof o === 'function';
      
      
      function  omitFrom(Arr, ...values) {
        if (values.length === 1) {
          let temp = [],
            string = is.String(Arr);
          if (isArraylike(Arr)) Arr = toArr(Arr)
          for (let i = 0, index = Arr.indexOf(values[0]); i < Arr.length; i++)
            if (i !== index) temp.push(Arr[i]);
          return string ? temp.join('') : temp;
        }
        values.forEach(val => Arr = omitFrom(Arr, val));
        return Arr;
      }
  
  
  root.observable = obj => {
    Object.defineProperty(obj,'listeners',{
      value : [],
      enumerable : false,
    });
    Object.defineProperty(obj,'removeListener',{
      value : function(fn) {
        if(isFunc(fn) && obj.listeners.includes(fn)) obj.listeners = omitFrom(obj.listeners,fn);
      },
      enumerable : false,
    });
    Object.defineProperty(obj,'listen',{
      get : function () {
        return obj.listeners[obj.listeners - 1];
      },
      set : function (func) {
        if(isFunc(func)) obj.listeners.push(func);
      },
      enumerable : false,
    });
    try {
      return new Proxy(obj,{
        get : function(target,key,reciever) {
          return target[key];
        },
        set : function(target,key,value,reciever) {
          target.listeners.forEach(fn => fn(target,key,value));
          return target[key] = value;
        }
      });
    } catch(e) {
      try {
        Object.observe(obj,changes => changes.forEach(change => {
          if(change.type === 'add' || change.type === 'update') obj.listeners.forEach(fn => fn(obj,change.name,obj[change.name]));
        }));
        return obj;
      } catch (e2) {}
    }
  }
  
})(document,self);

Hi. If I've read this right,

target.listeners.forEach(fn => fn(target,key,value));

...will fail if one of the listeners removes itself from listeners. The following listener will be skipped. I think you need to clone listeners before calling .forEach on it.

target.listeners.slice().forEach(...)