watch

watch

• Type: Object

• Details:

  An object where keys are expressions to watch and values are the corresponding callbacks. The value can also be a string of a method name, or an Object that contains additional options. The Vue instance will call $watch() for each entry in the object at instantiation.

• Example:

  var vm = new Vue({
    data: {
      a: 1
    },
    watch: {
      'a': function (val, oldVal) {
        console.log('new: %s, old: %s', val, oldVal)
      },
      // string method name
      'b': 'someMethod',
      // deep watcher
      'c': {
        handler: function (val, oldVal) { /* ... */ },
        deep: true
      }
    }
  })
  vm.a = 2 // -> new: 2, old: 1

• See also: Instance Methods - vm.$watch