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src/utils/scrollbar-width.js

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+import Vue from 'vue';
+
+let scrollBarWidth;
+
+export default function() {
+  if (Vue.prototype.$isServer) return 0;
+  if (scrollBarWidth !== undefined) return scrollBarWidth;
+
+  const outer = document.createElement('div');
+  outer.className = 'el-scrollbar__wrap';
+  outer.style.visibility = 'hidden';
+  outer.style.width = '100px';
+  outer.style.position = 'absolute';
+  outer.style.top = '-9999px';
+  document.body.appendChild(outer);
+
+  const widthNoScroll = outer.offsetWidth;
+  outer.style.overflow = 'scroll';
+
+  const inner = document.createElement('div');
+  inner.style.width = '100%';
+  outer.appendChild(inner);
+
+  const widthWithScroll = inner.offsetWidth;
+  outer.parentNode.removeChild(outer);
+  scrollBarWidth = widthNoScroll - widthWithScroll;
+
+  return scrollBarWidth;
+};