javascript - Promise 返回 'undefined' 或 babel 编译的代码不等待返回(async/await)

Question

有一个异步函数 (send)，其中如果未定义 msg 属性，则另一个函数 (getNextProcess) 设置其值。getNextProcess 在 Promise 中执行数据库查询。查询回调Promise解析函数。

问题:

用 Babel 翻译代码后，msg 将始终为“未定义”。Promise 在后台独立运行并返回正确的值(通过控制台日志检查)。

/* ORIGINAL */

class MyClass(){

    /*
        construct & other codes here...
    */

    getNextProcess(){
        new Promise(res => {
            logDb.get("SELECT * FROM process WHERE details NOT LIKE '%isComplete:true%' ORDER BY id LIMIT 1", (e, r) => {
                let result = JSON.parse(r.details);
                result.id = r.id;
                res(result);
            });
        });
    }

    async send(msg = undefined){
        if (!msg) msg = await this.getNextProcess();
        webView.send('webview:receive', msg);
    }

}

/* Transformed */
{
    key: "send",
    value: function () {
      var _send = (0, _asyncToGenerator2["default"])(
      /*#__PURE__*/
      _regenerator["default"].mark(function _callee() {
        var msg,
            _args = arguments;
        return _regenerator["default"].wrap(function _callee$(_context) {
          while (1) {
            switch (_context.prev = _context.next) {
              case 0:
                msg = _args.length > 0 && _args[0] !== undefined ? _args[0] : undefined;

                if (msg) {
                  _context.next = 5;
                  break;
                }

                _context.next = 4;
                return this.getNextProcess();

              case 4:
                msg = _context.sent;

              case 5:
                this.webView.send('webview:receive', msg);

              case 6:
              case "end":
                return _context.stop();
            }
          }
        }, _callee, this);
      }));

      function send() {
        return _send.apply(this, arguments);
      }

      return send;
    }()
}

/* package.json */
// ...
"scripts": {
    "start": "npm run compile && electron main.js",
    "compile": "browserify -t [ babelify --presets [ @babel/preset-env ] ] src/app.js -o js/app.js",
},
"devDependencies": {
    "@babel/core": "^7.4.5",
    "@babel/plugin-transform-async-to-generator": "^7.4.4",
    "@babel/plugin-transform-regenerator": "^7.4.5",
    "@babel/plugin-transform-runtime": "^7.4.4",
    "@babel/preset-env": "^7.4.5",
    "@babel/runtime": "^7.4.5",
    "babel-core": "^7.0.0-bridge.0",
    "babelify": "^10.0.0",
    "browserify": "^13.0.1",
    "electron": "^4.1.4",
    "electron-rebuild": "^1.8.5"
},
// ...

/* .babelrc */

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "useBuiltIns": "entry"
      }
    ]
  ],
  "ignore": [
    "../node_modules/jquery/dist/jquery.js"
  ],
  "plugins": [
    ["@babel/plugin-transform-runtime", {
      "helpers": true,
      "regenerator": true
    }],
    "@babel/plugin-transform-async-to-generator",
    "@babel/plugin-transform-regenerator",
  ]
}

Answer 1

看来您忘记了在 getNextProcess 中返回 promise 。如果你不给它一个 promise ，await就不知道要等待什么。

getNextProcess(){
    return new Promise(res => {
        //...
    });
}