<!-- parent component -->

<div @name="nue_add">
    sum: { a } + { b } = <sum :a="a" :b="b"></sum>
    <br />
    Ab: { a } + { b } = <Ab :a="a" :b="b"></Ab>
    <script>
        a = 10
        b = 100
        mounted() {
            console.info(this.$refs['sum'])
            console.info(this.$refs['Ab'])  //show undefined
        }
    </script>
</div>

<span @name="sum">
    { a + b }
</span>

<span @name="Ab">
    { a } { b }
</span>