|  Interactive Media Design

Methods

The logic for many event handlers will be too complex to keep inside the v-on directive. It is often more practical to bind or invoke a method from the Vue instance.

All methods are placed inside of the methods property of the Vue instance. When inside a method, the this keyword must be used to access data properties.

const app = Vue.createApp({
  data: function () {
    return { name: 'John' }
  },
  methods: {
    greeting: function () {
      // the this keyword is used access the data object
      if (this.name) {
        alert(`Hello ${this.name}`)
      } else {
        alert('Hello Friend.')
      }
    }
  }
})

const vm = app.mount('#app')

Binding Methods

To bind a method to a v-on directive, provide the method's name as the value.

<div id="app">
  <button v-on:click="greeting">Say Hello</button>
</div>

Invoking Methods

Instead of the binding methods directly, the v-on directive will also allow you to invoke methods as an inline JavaScript statement.

Invoking a method makes it possible to pass arguments, allowing for methods to be more flexible.

const app = Vue.createApp({
  data: function () {
    return { name: 'John' }
  },
  methods: {
    greeting: function (name) {
      if (name) {
        alert(`Hello ${name}`)
      } else if (this.name) {
        alert(`Hello ${this.name}`)
      } else {
        alert('Hello Friend.')
      }
    }
  }
})

const vm = app.mount('#app')

<div id="app">
  <button v-on:click="greeting('Jim')">Say Hello</button>
</div>

Event Object

When working with events, it is sometimes necessary to have direct access to the event object. Vue makes that possible by using the $event variable as an argument of the invoked method.

const app = Vue.createApp({
  el: `#app`,
  data: function () {
    return { name: 'John' }
  },
  methods: {
    greeting: function (name, event) {
      if (name) {
        alert(`Hello ${name}`)
      } else if (this.name) {
        alert(`Hello ${this.name}`)
      } else {
        alert('Hello Friend.')
      }
      
      alert(event.type)
    }
  }
})

const vm = app.mount('#app')

<div id="app">
  <button v-on:click="greeting('Jim', $event)">Say Hello</button>
</div>

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