我的节点js程序在读取json文件时给我一个"TypeError:无法读取未定义的属性'then'" [英] My node js program is giving me a "TypeError: Cannot read property 'then' of undefined", when reading a json file

问题描述

我正在尝试通过程序读取frpm的json文件文件夹，并且我想使用GET列表端点来浏览浏览器或邮递员，但是我遇到了上述TypeError.这是我的代码:

I'm trying to read frpm a json file folder withing my program and i want to use a GET list endpoint to read through browser or postman, but i'm getting the above TypeError. Here is my code:

model.js:

const fs = require('fs');

  function loadTeams() {
    return new Promise((resolve, reject) => {
      fs.readFile('./json/prov-nodes.json', (err, data) => {
          if (err) reject(err);
          const teams = JSON.parse(data);
          console.log(teams);
          resolve(teams);
      });
    });
}

app.use(bodyParser.json());

app.use(bodyParser.json());

app.get('/list', (req, res) => {
    let teams = [];
    loadTeams()
      .then(function(data){   
        teams = JSON.stringify(data); 
        console.log(teams);  
        **res.send(teams);** //intended to send to browser/postman response
        console.log('try...part ..read call');

      })
      .catch(error => console.log(error))
      res.send("My root page");
      console.log(teams);
     
});

推荐答案

loadTeams 函数不会返回promise，因此您无法调用 .then().

The loadTeams function does not return a promise, and therefore you cannot call .then().

您可以将函数包装在一个这样的Promise中:

You can wrap the function in a promise like this:

function loadTeams() {
    return new Promise(function(resolve, reject) {
        fs.readFile('./json/prov-nodes.json', (err, data) => {
            if (err) reject(err);
            try {
                const teams = JSON.parse(data);
                return resolve(teams);
            } catch(e) {
                reject(e);
            }
        });
    });
}

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