Transitioning from Global Namespace in JavaScript to TypeScript: A seamless migration journey

Question

Transitioning from Global Namespace in JavaScript to TypeScript: A seamless migration journey

I currently have a collection of files like:

library0.js
library1.js
...
libraryn.js

Each file contributes to the creation of a global object known as "MY_GLOBAL" similarly to this example:

library0.js

// Ensure the MY_GLOBAL namespace is available
if (typeof(MY_GLOBAL) === 'undefined') {
    var MY_GLOBAL = {};
}

MY_GLOBAL.TIMEOUT = 120000; // Represents 2 minutes

MY_GLOBAL.extractErrMsg = function(reqResponse) {
    console.log(reqResponse);
};

library1.js

// Ensure the MY_GLOBAL namespace is available
if (typeof(MY_GLOBAL) === 'undefined') {
    var MY_GLOBAL = {};
}

MY_GLOBAL.STRING = 'STRING';

MY_GLOBAL.exposed = function() {
    console.log("This is exposed");
};

In my current index.html file, I include all these files as script includes. As a result, any other JavaScript files can easily access:

MY_GLOBAL.extractErrMsg

or any other function/object within the MY_GLOBAL namespace.

I am in the process of transitioning to TypeScript and grappling with how to handle this global namespacing issue. Whenever I refer to the global object MY_GLOBAL, I encounter an error message TS2304: Cannot find name 'MY_GLOBAL'. Should I convert all of these to modules?

Appreciate your insights!

javascript typescript

Answer 1

Answer №1

If you're considering migration, TypeScript's namespace could be a valuable tool for your project. This feature allows TypeScript to compile namespaces into module-style JavaScript, maintaining the definition of MY_GLOBAL in the global scope while injecting it into functions for extension purposes. This means that you may not need to convert all of your JavaScript code right away.

For more information on TypeScript namespaces, visit: https://www.typescriptlang.org/docs/handbook/namespaces.html

lib0.ts

namespace MY_GLOBAL {
    export const TIMEOUT = 120000;
    export const extractErrMsg = reqResponse => console.log(reqResponse);
}

after compilation

var MY_GLOBAL;
(function (MY_GLOBAL) {
  MY_GLOBAL.TIMEOUT = 120000;
  MY_GLOBAL.extractErrMsg = function (reqResponse) { return 
  console.log(reqResponse); };
})(MY_GLOBAL || (MY_GLOBAL = {}));

lib1.ts

namespace MY_GLOBAL {
  export const STRING = 'STRING';
  export const exposed = () => console.log("This is exposed");
}

after compilation

var MY_GLOBAL;
(function (MY_GLOBAL) {
  MY_GLOBAL.STRING = 'STRING';
  MY_GLOBAL.exposed = function () { return console.log("This is exposed"); };
})(MY_GLOBAL || (MY_GLOBAL = {}));

Answer 2

If you're considering migration, TypeScript's namespace could be a valuable tool for your project. This feature allows TypeScript to compile namespaces into module-style JavaScript, maintaining the definition of MY_GLOBAL in the global scope while injecting it into functions for extension purposes. This means that you may not need to convert all of your JavaScript code right away.

For more information on TypeScript namespaces, visit: https://www.typescriptlang.org/docs/handbook/namespaces.html

lib0.ts

namespace MY_GLOBAL {
    export const TIMEOUT = 120000;
    export const extractErrMsg = reqResponse => console.log(reqResponse);
}

after compilation

var MY_GLOBAL;
(function (MY_GLOBAL) {
  MY_GLOBAL.TIMEOUT = 120000;
  MY_GLOBAL.extractErrMsg = function (reqResponse) { return 
  console.log(reqResponse); };
})(MY_GLOBAL || (MY_GLOBAL = {}));

lib1.ts

namespace MY_GLOBAL {
  export const STRING = 'STRING';
  export const exposed = () => console.log("This is exposed");
}

after compilation

var MY_GLOBAL;
(function (MY_GLOBAL) {
  MY_GLOBAL.STRING = 'STRING';
  MY_GLOBAL.exposed = function () { return console.log("This is exposed"); };
})(MY_GLOBAL || (MY_GLOBAL = {}));

Answer 3

Answer №2

If you don't want to rely on a global variable, consider exporting the values from your code instead. In the file named `library1.ts`, you can export constants like TIMEOUT set to 120000 and create a function extractErrMsg which logs the response:

// library1.ts

export const TIMEOUT = 120000;
export const extractErrMsg = reqResponse => console.log(reqResponse);

Then in your code that uses these values, you can import them as a module using:

import { TIMEOUT, extractErrMsg } from './library1';

Alternatively, you can use

import * as MY_GLOBAL from './libary1'

for one import at a time.

If modifying the code structure is not feasible yet, you can declare MY_GLOBAL and then import 'library1' to access its values:

// order here actually doesn't matter; you may want to do the import first
declare const MY_GLOBAL: any;
import './library1';

Afterwards, you are free to utilize the values from MY_GLOBAL. For more type safety, you can define a specific type instead of using any.

Answer 4

If you don't want to rely on a global variable, consider exporting the values from your code instead. In the file named `library1.ts`, you can export constants like TIMEOUT set to 120000 and create a function extractErrMsg which logs the response:

// library1.ts

export const TIMEOUT = 120000;
export const extractErrMsg = reqResponse => console.log(reqResponse);

Then in your code that uses these values, you can import them as a module using:

import { TIMEOUT, extractErrMsg } from './library1';

Alternatively, you can use

import * as MY_GLOBAL from './libary1'

for one import at a time.

If modifying the code structure is not feasible yet, you can declare MY_GLOBAL and then import 'library1' to access its values:

// order here actually doesn't matter; you may want to do the import first
declare const MY_GLOBAL: any;
import './library1';

Afterwards, you are free to utilize the values from MY_GLOBAL. For more type safety, you can define a specific type instead of using any.

Answer 5

Answer №3

If you ever find yourself in need, consider utilizing the method of importing * as MY_GLOBAL from './library1'. However, keep in mind that this can only be applied to one import at a time.

Building upon this concept, here is an example:

// global/file1.ts
export const TIMEOUT = 123

// global/file2.ts
export const bar = 456

// global/index.ts
export * from './file1'
export * from './file2'

// usage.ts
import * as MY_GLOBAL from './global'

Answer 6

If you ever find yourself in need, consider utilizing the method of importing * as MY_GLOBAL from './library1'. However, keep in mind that this can only be applied to one import at a time.

Building upon this concept, here is an example:

// global/file1.ts
export const TIMEOUT = 123

// global/file2.ts
export const bar = 456

// global/index.ts
export * from './file1'
export * from './file2'

// usage.ts
import * as MY_GLOBAL from './global'

Transitioning from Global Namespace in JavaScript to TypeScript: A seamless migration journey

library0.js

library1.js

Answer №1

Answer №2

Answer №3

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