Why Does This Typescript Output “[Class] is not a constructor.”?

Question

I\'m working in typescript 1.5 in visual studio. I have a main class called app.ts, and another called FizzBuzzManager.ts. I can\'t figure out what is wrong with this code,

Answer 1

It might be helpful to think about it as if you were writing the code in JavaScript directly. I came across this question because I got the same error in an Angular 2 test spec written in TypeScript. After thinking about it based on the answers above, I realized that JavaScript would have no idea what my equivalent to your BuzzFeed class was because it was at the bottom of the file.

I moved the class up to the top of the file before my first describe statement and everything works. Thought this might help others like myself.

Answer 2

TypeError: jim.FizzBuzzManager is not a constructor

This is a common error when you use --out : https://basarat.gitbook.io/typescript/main-1/outfile

You are responsible for loading the files in the right order. Don't use out and use external modules

Answer 3

When migrating from plain ES6 / Node.js using module.exports/require() it often happens to me that I forget to remove the old module.exports = <class> which also causes this error.

Answer 4

In my case I had the problem when I used babel with preset-env to compile TS-sources.

Works:

{
    "presets": ["@babel/typescript"],
    "plugins": [
        "@babel/proposal-class-properties",
        "@babel/proposal-object-rest-spread",
        "@babel/plugin-transform-runtime"
    ],
    "ignore": ["node_modules", "src/test"]
}

Wrong:

{
    "presets": [
        "@babel/typescript",
        [
            "@babel/preset-env",
            {
                "targets": {
                    "browsers": [
                        "last 2 Chrome versions",
                        "last 1 Safari versions",
                        "last 1 Firefox versions"
                    ]
                }
            }
        ]
    ],
    "plugins": [
        "@babel/proposal-class-properties",
        "@babel/proposal-object-rest-spread",
        "@babel/plugin-transform-runtime"
    ],
    "env": {
        "node": {
            "presets": [
                [
                    "@babel/preset-env",
                    {
                        "targets": {
                            "esmodules": true,
                            "node": "current"
                        },
                        "modules": "auto"
                    }
                ]
            ]
        }
    },

    "ignore": ["node_modules", "src/test"]
}

Answer 5

With JetBrains WebStorm, it's possible to get this error in your tests even if you have fixed a problem with imports in the code itself.

e.g. the following fix:

// import { Foo } from '@foo/bar';

import Foo = require('@foo/bar);

solved the issue, but it was necessary to run npm run compile or npm run test afterwards.

Then running the tests in WebStorm worked as expected.

Answer 6

at first, make sure that use

/// <reference path = "FizzBuzzManager.ts" />   

to refrence code to another .ts file at typescript root file

to compile typescript files that exist in different file.ts use this command

tsc --out app.js app.ts

because this command converts all typescript files into app.js