增加trimLeft和trimRight和trimStart和trimEnd的polyfill

package.json

@@ -15,6 +15,7 @@
   "browserslist": [
     "ie >= 9"
   ],
+  "sideEffects": ["src/polyfill.js"],
   "dependencies": {
     "@babel/polyfill": "^7.0.0",
     "@babel/runtime": "^7.0.0",

src/polyfill.js

+/* eslint-disable no-extend-native */
+import '@babel/polyfill';
+
+String.prototype.trimStart = String.prototype.trimStart ? String.prototype.trimStart : function trimStart() {
+  if (String.prototype.trimLeft) {
+    return this.trimLeft();
+  } else if (String.prototype.trim) {
+    const trimmed = this.trim();
+    const indexOfWord = this.indexOf(trimmed);
+    return this.slice(indexOfWord, this.length);
+  }
+};
+
+String.prototype.trimLeft = String.prototype.trimLeft ? String.prototype.trimLeft : String.prototype.trimStart;
+
+String.prototype.trimEnd = String.prototype.trimEnd ? String.prototype.trimEnd : function trimEnd() {
+  if (String.prototype.trimRight) {
+    return this.trimRight();
+  } else if (String.prototype.trim) {
+    const trimmed = this.trim();
+    const indexOfWord = this.indexOf(trimmed);
+    return this.slice(0, indexOfWord + trimmed.length);
+  }
+};
+
+String.prototype.trimRight = String.prototype.trimRight ? String.prototype.trimRight : String.prototype.trimEnd;

webpack.common.js

@@ -159,7 +159,7 @@ const cssRules = [
 const config = {
   context: path.resolve(__dirname),
   entry: {
-    polyfill: '@babel/polyfill',
+    polyfill: './src/polyfill.js',
     main: './src/index.js',
   },
   output: {