observable.js

// observable
// like ko.observable with subsciption

function ob(val){
  let lastVal = val;
  let callbacks = [];
  
  const accessor = function(setVal){
    if(setVal){
      lastVal = setVal;
      callbacks.forEach(c=> c(setVal));
    }
    else {
      return lastVal;  
    }
  }
  
  accessor.subscribe = function(callback){
    callbacks.push(callback);
  }
  
  return accessor;
}

Usage

// create with initial value
const name = ob('evren')

// read current value 
const strName = name()

// set new value
name('yortuc')

// subscribe to changes
name.subscribe(newVal => console.log(`my new name is ${newVal}`))