vue Error: Uncaught SyntaxError: Invalid shorthand property initializer

When defining an object using JSON format in JavaScript

An error occurred while debugging the browser: uncaught syntax error: invalid shorthand property initializer

<body>
    <div id=app>
        <button @click="handclick">Button</button>
        <p>{{name}}</p>
    </div>
</body>
<script src="./js/vue.js"></script>
<script>
    let app = new Vue({
        el: "#app",
        // The reason is that "=" should be written as ":"
        data: {
            name: "张三"
        },
        methods: {
            handclick() {
                this.name = 'lis'
            }
        },
        watch: {
            name(newVal, oldVal) {
                console.log(newVal, oldVal)
            }
        }
    })
</script>