javascript - Node.JS Express Promise 问题

Question

我正在开发 Node.JS/Express 应用程序。我使用 Jade 作为模板引擎。我遇到了一些奇怪的行为。

我有一个模拟 API，它向我的 Jade 模板返回一个简单的数组。我已经从服务器的 Angular 验证了 AP​​I 的工作原理。但是，每当我第一次启动服务器并进入该特定页面时，我都会收到错误消息

TypeError: Cannot read property 'length' of undefined
    at routes.js:28:34
    at Layer.handle [as handle_request] (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\layer.js:95:5)
    at next (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\route.js:131:13)
    at Route.dispatch (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\layer.js:95:5)
    at E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\index.js:277:22
    at Function.process_params (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\index.js:330:12)
    at next (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\index.js:271:10)
    at Function.handle (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\index.js:176:3)
    at router (E:\dev\code\javascript\ps_resume_express\node_modules\express\lib\router\index.js:46:12)

每次我启动服务器时都会发生这种情况。但是，只要它保持运行，后续调用就会工作并且页面会正确呈现。

这是我的路线方法是

router.get('/skills', (req, res) => {
      console.log('received request for skills');
      resumeAPI.getAllSkills().then((skills) => {
        console.log("inside then skills length " + skills.length);
        properties.skills = skills;
        console.log("inside then properties.skills length " + properties.skills.length);
      });
      console.log("outside promise skills length " + properties.skills.length);
      properties.heading = 'Skills';
      res.render('skills', properties)
    });

我在 console.log 行中 try catch 正在发生的事情。

我的API方法如下

class ResumeApi {
  static getAllSkills() {
    return new Promise((resolve, reject) => {
      console.log("from api skills " + skills.length);
      resolve(skills);
    });
  }
}

我可能做错了什么？

Answer 1

您的 console.log("outside promise skills length "+ properties.skills.length) 将在异步操作完成执行之前运行，所以不要期望它与未定义的不同。在这种情况下，您无法访问 promise 之外的 skills 属性。

需要将res.render放在.then()方法中执行getAllSkills()

router.get('/skills', (req, res) => {
  resumeAPI.getAllSkills().then((skills) => {
    properties.skills = skills;

    // res.render goes HERE, otherwise it will not have the skills property inside properties object
    properties.heading = 'Skills';
    res.render('skills', properties)
  });
});