watch Vuejs code example

Example 1: vue watch deep

export default {
  name: 'ColorChange',
  props: {
    colors: {
      type: Array,
      required: true,
    },
  },
  watch: {
    colors: {
      // This will let Vue know to look inside the array
      deep: true,

      // We have to move our method to a handler field
      handler(value) {
        console.log('The list of colors has changed!', value);
      }
    }
  }
}

Example 2: vuejs set

Vue.set(vm.someObject, 'propertyName', value)
// Or using alias
this.$set(this.someObject, 'propertyName', value)
// For an array, simply repalce propertyName with the index
this.$set(this.someArray, indexOfItem, value)
// Or assign new props to an object
this.someObject = Object.assign({}, this.someObject, { a: 1, b: 2 })

Example 3: vue watch

var vm = new Vue({
  el: '#demo',
  data: {
    firstName: 'Foo',
    lastName: 'Bar',
    fullName: 'Foo Bar'
  },
  watch: {
    firstName: function (val) {
      this.fullName = val + ' ' + this.lastName
    },
    lastName: function (val) {
      this.fullName = this.firstName + ' ' + val
    }
  }
})

Example 4: 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]
    }
  }
}
// ...

Example 5: 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('')
    }
  }
})

Example 6: vue add watcher

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