I'm a beginner at using js modules.
I'm working on a fairly simple web application. It uses typescript and angular 2, which heavily relies on modules.
Most of my app ts files 'import' one or many js modules (usually mostly angular 2 modules).
As I understand, because my app ts files have a top level 'import', they are automatically considered a js module by typescript.
However, I want any of my app ts files to be accessible by any other of my app ts files, without having to 'import' each other. But because they are now modules themselves, ts requires me to do that...
Is it possible?
It seems crazy to me that for each of my app ts file, I should have to declare every other of my app ts files that are used in there (I like to have tiny files with a single class/interface). In addition, this relies on relative paths which breaks as soon as I restructure my folder structure.
Am I thinking about this the wrong way?
You must have a js file which is an entry point to your application right?.. So in that file just import all the modules which you want to access without importing and attach them to the window object. Since the window object is available globally, you can access your module from anywhere without importing the corresponding module. For example,
Consider this scenario:
You have a module in a file called module1.ts
The entry point of your application is a file called index.ts
And you have a module2 where you require something from module1
// module1.ts
function add(first: number, second: number): number {
return first + second
}
export {add}
in your index.ts
// index.ts
import {add} from '<path to module1>/module1';
window.add = add
Now in your module2
// module2.ts
window.add(1, 2)
Since the window object is available globally you can attach as many properties to it as you like.
As far as the type resolution is concerned you can declare a window module with the add function you require in a .d.ts file as follows:
declare module window {
add: (first: number, second: number) => number
}
Declaring dependencies (e.g modules) for each file is a double-edged sword.
The advantage is that there is no 'magic' - you know exactly where each function, variable, class etc. is coming from. This makes it much easier to know what libraries / frameworks are being used and where to look to troubleshoot issues. Compare it to opposite approach that Ruby on Rails uses with Ruby Gems, where nothing is declared and everything is auto-loaded. From personal experience I know it becomes an absolute pain to try to workout where some_random_method is coming from and also what methods / classes I have access to.
You're right that the disadvantage is that it can become quite verbose with multiple imports and moving relative files. Modern editors and IDEs like WebStorm and Visual Studio Code have tools to automatically update the relative paths when you move a file and also automatically add the imports when you reference code in another module.
One practical solution for multiple imports is to make your own 'group' import file. Say you have a whole bunch of utility functions that you use in all your files - you can import them all into a single file and then just reference that file everywhere else:
//File: helpers/string-helpers.ts
import {toUppercase} from "./uppercase-helper";
import {truncate} from "./truncate-helper";
export const toUppercase = toUppercase;
export const truncate = truncate;
Then in any other file:
import * as StringHelpers from "../path-to/helpers/string-helpers";
...
let shoutingMessage = StringHelpers.toUppercase(message);
The disadvantage of this is that it may break tree shaking, where tools such as webpack remove unused code.
Is it possible
Not in any easy way. The ts file is a module and uses e.g. module.exports (if commonjs) that will need to be shimmed out. And that is just the runtime story. The TypeScript story will be harder and one way would be to make a .d.ts file for the module stating the contents as global.
Like I said. Not worth doing. Modules are the way forward instead of making something hacky.
It's not crazy at all. You are definitively thinking in the wrong way.
Actually what you don't like it's a common feature in all modern programming languages and it makes the code and structure of the app a lot clearer and simple to understand.
Without imports and going to old school way looks very crazy to me :)
You can have only chaos with so many global variables.
Related
I'm working in a web development project.
Right now i'm using a 3rd party library to instantiate an object of that library in a file called, let's say, fileA.js
so i do:
import libraryExport from "./librarymain.js"
var object = libraryExport( ... );
export default object;
Now, in fileB.js i want to use the methods that the instantiated object has, for example:
import object from "fileA.js"
object.methodOfTheLibrary();
However, when im running this in my browser console i always get "methodOfTheLibrary is not a function", which means, from my point of view, that the library is not being imported properly in fileB.js
Note: I'm using webpack to bundle all of my files and everything was compiling and bundling just fine until i came with issues. I usually know my way around C++ in an advanced way but for JS i just still don't fully understand how to solve these kind of import issues.
Thank you for any help
It's generally* recommended that you avoid using an imported module directly in the body of another module. (One of your own modules, that is... as you'll see in a moment, third-party modules are generally fine to use.)
The big issue is load order. If your fileA also imports some other module, which imports another module which then imports fileB, then fileB will attempt to run and, since fileA is still trying to load dependencies, object will not actually have been instantiated yet.
You'll either need to carefully review your dependencies to look for just such a loop and then eliminate it or, if possible, restructure fileA to wrap your code in a function that can be called once the entry point has finished loading (which will guarantee that all other modules have been resolved):
// fileB.js
import object from "fileA.js"
export function init() {
object.methodOfTheLibrary();
}
// main.js
import init from "fileB.js";
init();
* "generally" meaning that there are plenty of perfectly acceptable situations where it's fine. You just have to mindful of the pitfalls and mitigate against those situations.
I am building a web application.
I use typescript for the client side and golang for the server side.
I use typescript 3.9.2.
I want to compile the .ts files to .js, and use modules.
The default compiling compile it to CommonJS module loader.
Then in the browser it has some exports.__... in the second line.
I searched and it basicly said it want a variable called exports, which I don't have. In this case, I don't like the main solution to define a mock exports in other script tag.
I changed the compilerOption to "module":"ES6"
and then it compile and loaded well (after changing the type of the script to module), but the browser can't find the module i want to import.
The code goes like this:
use.ts
import * as fun from 'funcs'
let bar = fun.foo()
funcs.ts
export function foo() :boolean{
return true;
}
use.js
import * as fun from 'funcs'
var bar = fun.foo()
funcs.js
export function foo(){
return true;
}
And now the browser can't find /funcs, which it needs for the use.js. When i change manualy the first line in use.js to
import * as fun from 'funcs.js'
It works.
What can i do to make everything automatic?
What is the best practice here?
ES Module imports need to have the .js extension, but Typescript's modules don't and right now there does not appear to be a built-in option to add them automatically, but somebody did write a script to add the extensions to the imports, or you can add them to the imports manually.
There is some discussion on the TypeScript Github about this and related issues. They are considering adding a module resolution option to the compiler for the browser.
This is just something I thought today and I didn't see a lot of information so I'm going to share this weird cases and how I personally solved them (if there's a better way please comment, but meanwhile this might help others ^^)
In a regular module, you would do something like this to export your function/library/object/data:
// regular NodeJS way:
module.exports = data;
// ES6 way
// (will get transpiled to the regular way using the module variable by webpack)
export data;
default export data;
When compiling the library usually babel or tsc are used, but if for any reason you want not only to compile (transpile) your library but also pack it using webpack, you will encounter this case.
As you know, in a webpack bundle the module variable is local to the bundle (every module/file gets wrapped with a function where module is a parameter = local variable), so nothing really gets exported outside the bundle, is just nicely managed by webpack.
That means that you can't also access the contents using the regular require/import methods.
In some case you might find necessary to export outside webpack. (i.e. you are trying to build a library using webpack and you want it to be accessible by other people). This basically means you need to access the original module variable, but webpack doesn't expose it like it happened with __non_webpack_require__.
See also: Importing runtime modules from outside webpack bundle
The solution is to create our own __non_webpack_module__ (as webpack does with __non_webpack_require__.
How I did it is using webpack.BannerPlugin to inject some code outside the bundle. This code is prepended to the build after the minification is done, so it's preserved safely.
In your webpack.config.js:
plugins: [
new BannerPlugin({
raw: true,
banner: `const __non_webpack_module__ = module;`,
}),
]
And again, if you are using TypeScript, in global.d.ts:
declare const __non_webpack_module__: NodeModule;
And now, you can do something like this in your code:
__non_webpack_module__.exports = /* your class/function/data/whatever */
This will allow to import it as usual from other files
Tip: You might want to look at BannerPlugin to check other options, like include or exclude so this variable is only generated on the desired files, etc.
Is it possible to configure ESLint in WebStorm so functions, variables, etc. are parsed also from files in the same folder? In my build process, I concatenate all files in the same folders into big closures, for example:
src/
main/ ===> "main.js"
api.js
init.js
ui.js
constants.js
.
.
renderer/ ===> "renderer.js"
core.js
events.js
I would like ESLint to treat all those files just like one, so I don't get "undef" errors for things that are defined.
If it can't be done automatically, I wouldn't mind to create a manual configuration specifying all those files if that is possible.
EDIT: Why I don't (can't) use modules? TLDR- legacy code and project requirements.
I need to minify all code. Current closure compiler can transpile ES6 into ES5, but I found some ES6 features very prone to produce broken code. So I am forced to use ES5.
As I need ES5. I would only be able to use require() to use modules. Now that's a problem, as require() is a dynamic include and it impacts performance on my context (big electron app for modest power devices)
So to answer #Avin_Kavish, I agree what I do is "technically non conforming", but at the end of the build process it is, because each folder has been grouped into a file. That file is the module or the script. To group the files I use a Gradle plugin https://github.com/eriwen/gradle-js-plugin, I inject a "closure header" and a "closure footer", and all the files in between in the order I want.
Despite the inconvenience, at the end I get super-compact nodeJS code, with all methods obfuscated, etc.
I ended up using #Patrick suggestion, thanks for that!
EDIT 2
WebPack + Electron-WebPack turned out to be what I was looking for.
BTW- I think the proper way to do this is if EsLint would allow a "folder" sourceType.
You didn't provide code examples in your question, but I assume you do something like this:
api.js
const api = {
fetchData() {
// some code that fetches data
}
};
core.js
const core = {
init() {
api.fetchData();
}
};
The ESLint rule that causes errors when you lint these JavaScript modules is the no-undef rule.
It checks for variables that are used without having been defined. In the code example core.js above, this would be api, because that is defined in another module, which ESLint doesn't know about.
You don't care about these errors, because in your actual JS bundle used in production, the code from api.js and core.js is concatenated in one bundle, so api will be defined.
So actually api in this example is a global variable.
The no-undef rule allows you to define global variables so that they won't cause errors.
There are two ways to do this:
Using Comments
At the beginning of your core.js module, add this line:
/* global api */
Using the ESLint Config
As explained here – add this to your .eslintrc file:
{
"globals": {
"api": "writable"
}
}
Side Note
As some commenters to your question pointed out, it would probably be better to use import and export statements in the modules, together with a module bundling tool like webpack to create one bundle from your JavaScript modules.
A physical JavaScript file with an import/export statement is a module by the standard. A single .js file without import/export is a script by the standard. What you are trying to do is non-conforming to this, there is no specification in ECMAScript that allows splitting a single script or module across several files. I do get where you are coming from, for example: C# has partial classes that allows you to split a class across multiple files. But trying to replicate this without a standard syntax is not wise. Especially, when import/export can and will do the job for you
For example, with the following assumptions, your main.js can be refactored to,
constants.js // <--- constants
ui.js // <--- logic to build UI
api.js // <--- exposing public api
init.js // <--- setup code before use
// main.js
// If you name this index.js you can import it as 'src/main' instead of 'src/main/main.js'
import { A,B } from './constants'
import { api } from './api'
import { displayUi } from './ui'
import { init } from './init'
init(A);
displayUi(B);
export { api } // <-- re-expose public api
I do own quite a big code basis implemented in JavaScript based on NodeJS. I do want to give typescript a try and want to implement all new modules in typescript. Just to see how it performs and how I like the idea. I do need to be able to revert back at any time so I do not want to put to much effort into the migration.
I started by using WebStorm and Gulp to support typescript. I created a new module and used the import / require combination.
import settings = require("./settings");
import _ = require("lodash-node");
By doing so I receive a couple of errors.
Error:(22, 27) TS2307: Cannot find external module './settings'.
Error:(23, 20) TS2307: Cannot find external module 'lodash-node'.
Those modules have no typescript definition file and are plain javascript modules (lodash is obviously a external library). I do have a couple of dependencies and I do not want to create definitions manually even if they are just empty stubs. As mentioned I do want to keep the integration as simple as possible.
Is there a general flag or something like that I can set?
The easiest way to proceed (if you don't want type information for a module) is to write:
declare module "lodash-node" {
var notTyped: any; // naming is unimportant here
export = notTyped;
}
Put that in a separate .d.ts file and /// <reference> it. Then _ will be of type any in your implementation file and the compiler won't complain about not know what module you're talking about.
You can use webpack's typescript-loader and start from there. Make sure you put target: 'node' on your webpack config so you don't have all the browser junk.