Answers for "computed vs watch vue"

computed vue

// ...
computed: {
  fullName: {
    // getter
    get: function () {
      return this.firstName + ' ' + this.lastName
    },
    // setter
    set: function (newValue) {
      var names = newValue.split(' ')
      this.firstName = names[0]
      this.lastName = names[names.length - 1]
    }
  }
}
// ...

vue computed

var vm = new Vue({
  el: '#example',
  data: {
    message: 'Hello'
  },
  computed: {
    // a computed getter
    reversedMessage: function () {
      // `this` points to the vm instance
      return this.message.split('').reverse().join('')
    }
  }
})

vue add watcher

vm.$watch('person.name.firstName', function(newValue, oldValue) {
	alert('First name changed from ' + oldValue + ' to ' + newValue + '!');
});

computed vs watch vue

Differences and Similarities
	Let's see how they are different:

        	Computed props are more declarative than watched properties
            
        	Computed props should be pure: return a value, synchronous, and 
        have no side-effects
        
        	Computed props create new reactive properties, watched props only 
        call functions
        
        	Computed props can react to changes in multiple props, whereas 
        watched props can only watch one at a time.
        
        	Computed props are cached, so they only recalculate when things 
        change. Watched props are executed every time
        
        	Computed props are evaluated lazily, meaning they are only 
        executed when they are needed to be used. Watched props are executed 
        whenever a prop changes

  	But they also have some similarities
    
	They aren't exactly twins, but they both:

          React to changes in properties
          Can be used to compute new data
          
    Watch is for side effects. If you need to change state you want to use a computed prop instead.

	Most of the time you'll want a computed prop, so try to use that first. 
    If it doesn't work, or results in weird code that makes you feel like 
    taking a shower, then you should switch to using a watched prop.