Why is my Typescript code not functioning properly even after including the reference path?

Question

Why is my Typescript code not functioning properly even after including the reference path?

I recently created two files:

main.ts:

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

welcome();

external.ts

var welcome = function() {
    console.log("hi there");
}

After compiling both files to JavaScript and running them using the command: $ node main.js

I was surprised when the 'welcome' function didn't execute as expected. Instead, I encountered an error:

ReferenceError: welcome is not defined

Upon researching about triple-slash directive (https://www.typescriptlang.org/docs/handbook/triple-slash-directives.html), it was mentioned that:

The compiler does a preprocessing pass on input files to resolve all triple-slash reference directives. This process includes adding additional files to compilation.

Despite this explanation, I still struggle to comprehend why the function from external.ts file couldn't be accessed.

typescript

Answer 1

Answer №1

If you are working in a Node environment, the approach mentioned above won't work as-is. You'll need to import (require) the file in order to use it with Node.

Here's what you need to do:

// external.js
export var hello = function() {
    console.log("hello");
}

And then use it like this:

// main.js

const { hello } = require("./external");

hello();

Additionally, when compiling your code, make sure to compile it for Node by using:

tsc -m commonjs ./main.ts

Answer 2

If you are working in a Node environment, the approach mentioned above won't work as-is. You'll need to import (require) the file in order to use it with Node.

Here's what you need to do:

// external.js
export var hello = function() {
    console.log("hello");
}

And then use it like this:

// main.js

const { hello } = require("./external");

hello();

Additionally, when compiling your code, make sure to compile it for Node by using:

tsc -m commonjs ./main.ts

Answer 3

Answer №2

The main purpose of a reference file is to describe the various functions, types, and interfaces available in a program without diving into their implementation details.

It focuses more on declaration rather than implementation, providing guidance for the compiler to understand the structure of the code.

For example, if we take a look at a simple scenario in a file named main.ts, where the following code snippet is present:

console.log('hi')

Without the required @types/node package, the compilation process would fail as the compiler wouldn't recognize the 'console' object. This is why having reference files becomes crucial:

- By including reference files, we are essentially informing the compiler that there exists a 'console' object with a 'log' method.

In practice, you can create a declaration in a file like hello.d.ts:

declare function hello(): void;

and then refer to it in your hello.ts file:

/// <reference path="./hello.d.ts" />

hello();

As a result, when you compile the code using tsc hello.ts, the compiler successfully recognizes 'hello' as a function that can be invoked.

Nevertheless, running the script through node hello.js may lead to a ReferenceError since, technically speaking, the 'hello()' function is not implemented by the node engine during runtime.

One way to see this in action is by trying something like:

console.log('hello')

This statement will execute correctly because it's an engine-provided function, aiding in better comprehension of the concept.

Answer 4

The main purpose of a reference file is to describe the various functions, types, and interfaces available in a program without diving into their implementation details.

It focuses more on declaration rather than implementation, providing guidance for the compiler to understand the structure of the code.

For example, if we take a look at a simple scenario in a file named main.ts, where the following code snippet is present:

console.log('hi')

Without the required @types/node package, the compilation process would fail as the compiler wouldn't recognize the 'console' object. This is why having reference files becomes crucial:

- By including reference files, we are essentially informing the compiler that there exists a 'console' object with a 'log' method.

In practice, you can create a declaration in a file like hello.d.ts:

declare function hello(): void;

and then refer to it in your hello.ts file:

/// <reference path="./hello.d.ts" />

hello();

As a result, when you compile the code using tsc hello.ts, the compiler successfully recognizes 'hello' as a function that can be invoked.

Nevertheless, running the script through node hello.js may lead to a ReferenceError since, technically speaking, the 'hello()' function is not implemented by the node engine during runtime.

One way to see this in action is by trying something like:

console.log('hello')

This statement will execute correctly because it's an engine-provided function, aiding in better comprehension of the concept.

Why is my Typescript code not functioning properly even after including the reference path?

Answer №1

Answer №2

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