1.安装依赖
yarn add react-app-polyfill
遇到的问题：引入依赖后，造成我的postcss-px2rem 配置失效，样式会乱掉，重新配置一下postcss-px2rem 即可（推荐postcss-px2rem-exclude）；
2. 在src/index.js的最顶部引入
import "react-app-polyfill/ie11";
import "react-app-polyfill/stable";
3.在packge.json文件下 browserlist 添加ie11
"browserslist": {
"production": [
">0.2%",
"not dead",
"not op_mini all",
"ie 11"
],
"development": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version",
"ie 11"
]
}
