change code structure

src/tooltipMixin.js

@@ -0,0 +1,19 @@
+export default {
+  data () {
+    return {
+      tooltipStyle: {
+        visibility: 'hidden'
+      }
+    }
+  },
+  methods: {
+    showTooltip (e) {
+      this.tooltipStyle.top = e.clientY - 12 + 'px'
+      this.tooltipStyle.left = e.clientX + 12 + 'px'
+      this.tooltipStyle.visibility = 'visible'
+    },
+    hideTooltip () {
+      this.tooltipStyle.visibility = 'hidden'
+    }
+  }
+}