Learning Notes 0630 - babel & babel cli

今天上午，探索一下使用babel来编译一个jsx。有关这部分功能改变的介绍：New jsx transform in React 17

安装babel cli (not global)

npm install --save-dev @babel/core @babel/cli

需要npm install 下面两个presets里面的包， 创建一个babel.config.json

{
    "presets":["@babel/preset-env","@babel/preset-react"],
    "plugins":[]
}

使用cli编译一个jsx文件

npx babel xxx.jsx --out-file yyy.js

就能输出编译好的jsx了

jsx文件，实现一个简单的组件

import { useState } from "react"

function Hello(){
    const [s,setsts]=useState(0)
    return <>{s}</>
}

babel transpiled:

"use strict";

var _react = require("react");
function _slicedToArray(r, e) { return _arrayWithHoles(r) || _iterableToArrayLimit(r, e) || _unsupportedIterableToArray(r, e) || _nonIterableRest(); }
function _nonIterableRest() { throw new TypeError("Invalid attempt to destructure non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); }
function _unsupportedIterableToArray(r, a) { if (r) { if ("string" == typeof r) return _arrayLikeToArray(r, a); var t = {}.toString.call(r).slice(8, -1); return "Object" === t && r.constructor && (t = r.constructor.name), "Map" === t || "Set" === t ? Array.from(r) : "Arguments" === t || /^(?:Ui|I)nt(?:8|16|32)(?:Clamped)?Array$/.test(t) ? _arrayLikeToArray(r, a) : void 0; } }
function _arrayLikeToArray(r, a) { (null == a || a > r.length) && (a = r.length); for (var e = 0, n = Array(a); e < a; e++) n[e] = r[e]; return n; }
function _iterableToArrayLimit(r, l) { var t = null == r ? null : "undefined" != typeof Symbol && r[Symbol.iterator] || r["@@iterator"]; if (null != t) { var e, n, i, u, a = [], f = !0, o = !1; try { if (i = (t = t.call(r)).next, 0 === l) { if (Object(t) !== t) return; f = !1; } else for (; !(f = (e = i.call(t)).done) && (a.push(e.value), a.length !== l); f = !0); } catch (r) { o = !0, n = r; } finally { try { if (!f && null != t["return"] && (u = t["return"](), Object(u) !== u)) return; } finally { if (o) throw n; } } return a; } }
function _arrayWithHoles(r) { if (Array.isArray(r)) return r; }
function Hello() {
  var _useState = (0, _react.useState)(0),
    _useState2 = _slicedToArray(_useState, 2),
    s = _useState2[0],
    setsts = _useState2[1];
  return /*#__PURE__*/React.createElement(React.Fragment, null, s);
}

注意最后的React.createElement