<div id="app">
{{a}}
{{b}}
<button @click="add">add</button>
</div>var vm = new Vue({
el: '#app',
data: {
a: 1,
b: 1
},
methods: {
add() {
this.a += 1;
}
}
});
vm.$data.a = 2; // equal to vm.a = 2
vm.$watch('a', function (newValue, oldValue) {
this.b = oldValue;
});
External CSS
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