Typescript compiled js files throw exception on undefined default property

Question

Cannot read property 'json' of undefined

at Object. (C:\web\learnTypescript\dist\index.js:7:40)

dist/index.js:7

app_1.default.use(body_parser_1.default.json());

I created a simple project to learn TypeScript. I have my dependencies and their @types counterparts installed but I continue to get the above error when I try to start node node dist/index.js.

tsconfig.json

{
    "compilerOptions": {
        "allowSyntheticDefaultImports": true,
        "moduleResolution": "node",
        "module": "commonjs",
        "target": "es6",
        "outDir": "dist"
    },
    "include": [ "src/**/*" ],
    "exclude": [ "node_modules" ]
}

src/index.ts

import app from './app'
import bodyParser from 'body-parser'
/* more imports */

app.use(bodyParser.json());
/* more code follows */

dist/index.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const app_1 = require("./app");
const body_parser_1 = require("body-parser");
/* more requires */
app_1.default.use(body_parser_1.default.json());
/* more code follows */

What if you change this to import * as bodyParser from 'body-parser';? — Tim B James
– Tim B James, Commented Oct 31, 2017 at 11:06
That did it. Please add that as the answer and I'll give you credit. I some question around why I need to import that way, but I'll save that for your answer for documentation purposes. Thank you. — bflemi3
– bflemi3, Commented Oct 31, 2017 at 11:16

Tim B James · Accepted Answer · 2017-10-31 11:36:16Z

1

If you change your import to be;

import * as bodyParser from 'body-parser';

Then that should fix it.

* as syntax is known as a namespace import, and effectively creates 1 variable which contains everything within the file.

There are a few ways you can import from a file depending on the exports from the other file.

file1.ts

export default class Foo {
}

export class Bar {
}

const a = 'Hello';

export { a as A }

file2.ts

import A from 'file1'; // A is now the default export from file1
import * as File from 'file1'; // File is now a constant with Foo, Bar and A
import { Bar } from 'file1'; // Importing only Bar from file1

As James has also mentioned, you can also use the code; import { json } from 'body-parser';

edited Oct 31, 2017 at 11:36

answered Oct 31, 2017 at 11:29

Tim B James

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1 Comment

James Over a year ago

Seems unnecessary, should tree shake and do import { json } from 'body-parser'

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