05_computed_properties.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    p{
        color: red;
    }
</style>
<body>
    <div id="app">
        <h1>{{ getLength }}</h1>
        <h1>{{ message }}</h1>
        <h1>{{ reverse }}</h1>
        <button @click='show'>Click</button>
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.14/dist/vue.js"></script>
    <script>
        let app = new Vue({
            el: '#app',
            data: {
               message: 'hello world'
            },
            computed: {
                getLength() {
                    return this.message.length; //must return
                },
                reverse() {
                    let newMessage = this.message.split("");
                    let reverseMessage = newMessage.reverse().join("");
                    return reverseMessage;
                    // return this.message.split("").reverse().join("")
                }
            },
            methods: {
               show() {
                   alert(this.message.length)
               }
            }
        })
    </script>
</body>
</html>