I have a TypeScript application working with es16 modules, most of them are imported statically. I want to use a (validator-) module now that is only imported in debug mode. It's all working, but I don't understand how to type things so that I get code completion and error-checking.
in my main class in main.ts I have:
...
if(debug){
import('./validator.js').then((module) => this.validate(module))
}
...
the validate method looks like that:
private validate(module):void{
new module.Validator(dataToValidate);
}
validator.js contains:
export class Validator{
coonstructor(data:MyDatatype){
stuff going on here...
}
}
what I would like to know/do is:
in the validate method:
private validate(module:someMeaningfulType){...}
and also I'd like to import the Validator class, without actually importing it.
if I wrote
import {Validator} from './validate.ts'
at the top of main.ts I would load the file regardles of I need it, which defeats the whole point of dynamic imports.
I might try to whrite a type declartaion for module and Validator in main.ts, but even if that wouldn't conflict somehow, I would have to manually keep it in sync with the actual module, which is not what I want - obviously.
I might miss something obvious, but I cannot find out what. I find id hard to search for the (pure) use of native es2020/2022 modules with Typescrit, as there is so much information about node-modules etc. overshadowing it.
You can actually use import with typeof to get the type of the imported module:
private validate(module: typeof import("./validator.js")) { ... }
Alternatively, you can use a type-only import, which will be erased in the output:
import type * as ValidatorModule from "./validator.js";
// ...
private validate(module: ValidatorModule) { ... }
I have a config.ts and I do
module.exports = { something: 123 }
when I import like import { something } from './config.ts' I got error of config.ts' is not a module, what's the issue? my typescript is configured rightly and it's working in other places.
If you're using import { something } from './config.ts', you're using JavaScript modules, but your code in config.ts is using CommonJS modules. Some bundlers and such may let you mix them, but it's best not to.
To make config.ts a JavaScript module compatible with that import declaration (which expects a named export called something), change it to:
export const something = 123;
Or, of course, to use config.ts via CommonJS, your code using it would be:
const { something } = require("./config.ts");
...but given the error you're getting, I think your project is set up to use JavaScript modules (import/export), which here in almost 2021 is probably best (now that we have dynamic import to handle the cases where static modules don't quite do the job).
I'm using web pack to package a library.
We have multiple ES6 classes, in this fashion:
/src/Lib.js
import HelperClass from './HelperClass.js';
class Lib {
method1() {...}
}
/src/HelperClass.js
class HelperClass {
doSth() {...}
}
Packaging with webpack works, we end up with one file lib.js that contains Lib and HelperClass as var Lib = ....
How can I hide the HelperClass from the global namespace (e.g. make it a private class) with webpack?
UPDATE:
Now I'm running into an issue with importing the HelperClass! I uploaded a sample project https://github.com/benmarten/webpack_es6_test
This line:
__WEBPACK_IMPORTED_MODULE_0__Helper_js___default.a.doSth();
results in:
[Error] TypeError: __WEBPACK_IMPORTED_MODULE_0__Helper_js___default.a.doSth is not a function. (In '__WEBPACK_IMPORTED_MODULE_0__Helper_js___default.a.doSth()', '__WEBPACK_IMPORTED_MODULE_0__Helper_js___default.a.doSth' is undefined)
method1 (lib.js:92)
Global Code (index.htm:6)
When creating a library with webpack you expose everything that is exported in your entry point, everything else is not accessible from outside but you can use it within your code. If you want to use anything from another file, you still need to export it, because the files are still modules. Just because there is an export, does not mean it becomes a global. Only the exports in the entry specified in the webpack.config.js will be exposed.
Export the Helper in HelperClass.js:
class Helper {
static doSth() {
console.log('helper:doSth');
}
}
export default Helper;
Then import it in Lib.js:
import Helper from './HelperClass.js';
class Lib {
static method1() {
Helper.doSth();
}
}
export default Lib;
Now the default export of your bundle will be the Lib class and you can use Helper inside it without exposing it.
You should also read the Authoring Libraries Guides.
I am using TypeScript 1.6 with ES6 modules syntax.
My files are:
test.ts:
module App {
export class SomeClass {
getName(): string {
return 'name';
}
}
}
main.ts:
import App from './test';
var a = new App.SomeClass();
When I am trying to compile the main.ts file I get this error:
Error TS2306: File 'test.ts' is not a module.
How can I accomplish that?
Extended - to provide more details based on some comments
The error
Error TS2306: File 'test.ts' is not a module.
Comes from the fact described here http://exploringjs.com/es6/ch_modules.html
17. Modules
This chapter explains how the built-in modules work in ECMAScript 6.
17.1 Overview
In ECMAScript 6, modules are stored in files. There is exactly one
module per file and one file per module. You have two ways of
exporting things from a module. These two ways can be mixed, but it is
usually better to use them separately.
17.1.1 Multiple named exports
There can be multiple named exports:
//------ lib.js ------
export const sqrt = Math.sqrt;
export function square(x) {
return x * x;
}
export function diag(x, y) {
return sqrt(square(x) + square(y));
}
...
17.1.2 Single default export
There can be a single default export. For example, a function:
//------ myFunc.js ------
export default function () { ··· } // no semicolon!
Based on the above we need the export, as a part of the test.js file. Let's adjust the content of it like this:
// test.js - exporting es6
export module App {
export class SomeClass {
getName(): string {
return 'name';
}
}
export class OtherClass {
getName(): string {
return 'name';
}
}
}
And now we can import it in these three ways:
import * as app1 from "./test";
import app2 = require("./test");
import {App} from "./test";
And we can consume imported stuff like this:
var a1: app1.App.SomeClass = new app1.App.SomeClass();
var a2: app1.App.OtherClass = new app1.App.OtherClass();
var b1: app2.App.SomeClass = new app2.App.SomeClass();
var b2: app2.App.OtherClass = new app2.App.OtherClass();
var c1: App.SomeClass = new App.SomeClass();
var c2: App.OtherClass = new App.OtherClass();
and call the method to see it in action:
console.log(a1.getName())
console.log(a2.getName())
console.log(b1.getName())
console.log(b2.getName())
console.log(c1.getName())
console.log(c2.getName())
Original part is trying to help to reduce the amount of complexity in usage of the namespace
Original part:
I would really strongly suggest to check this Q & A:
How do I use namespaces with TypeScript external modules?
Let me cite the first sentence:
Do not use "namespaces" in external modules.
Don't do this.
Seriously. Stop.
...
In this case, we just do not need module inside of test.ts. This could be the content of it adjusted test.ts:
export class SomeClass
{
getName(): string
{
return 'name';
}
}
Read more here
Export =
In the previous example, when we consumed each validator, each module only exported one value. In cases like this, it's cumbersome to work with these symbols through their qualified name when a single identifier would do just as well.
The export = syntax specifies a single object that is exported from the module. This can be a class, interface, module, function, or enum. When imported, the exported symbol is consumed directly and is not qualified by any name.
we can later consume it like this:
import App = require('./test');
var sc: App.SomeClass = new App.SomeClass();
sc.getName();
Read more here:
Optional Module Loading and Other Advanced Loading Scenarios
In some cases, you may want to only load a module under some conditions. In TypeScript, we can use the pattern shown below to implement this and other advanced loading scenarios to directly invoke the module loaders without losing type safety.
The compiler detects whether each module is used in the emitted JavaScript. For modules that are only used as part of the type system, no require calls are emitted. This culling of unused references is a good performance optimization, and also allows for optional loading of those modules.
The core idea of the pattern is that the import id = require('...') statement gives us access to the types exposed by the external module. The module loader is invoked (through require) dynamically, as shown in the if blocks below. This leverages the reference-culling optimization so that the module is only loaded when needed. For this pattern to work, it's important that the symbol defined via import is only used in type positions (i.e. never in a position that would be emitted into the JavaScript).
Above answers are correct. But just in case...
Got same error in VS Code. Had to re-save/recompile file that was throwing error.
How can I accomplish that?
Your example declares a TypeScript < 1.5 internal module, which is now called a namespace. The old module App {} syntax is now equivalent to namespace App {}. As a result, the following works:
// test.ts
export namespace App {
export class SomeClass {
getName(): string {
return 'name';
}
}
}
// main.ts
import { App } from './test';
var a = new App.SomeClass();
That being said...
Try to avoid exporting namespaces and instead export modules (which were previously called external modules). If needs be you can use a namespace on import with the namespace import pattern like this:
// test.ts
export class SomeClass {
getName(): string {
return 'name';
}
}
// main.ts
import * as App from './test'; // namespace import pattern
var a = new App.SomeClass();
In addition to A. Tim's answer there are times when even that doesn't work, so you need to:
Rewrite the import string, using the intellisense. Sometimes this fixes the issue
Restart VS Code
I had this issue and I had forgotten to export the Class.
In addition to Tim's answer, this issue occurred for me when I was splitting up a refactoring a file, splitting it up into their own files.
VSCode, for some reason, indented parts of my [class] code, which caused this issue. This was hard to notice at first, but after I realised the code was indented, I formatted the code and the issue disappeared.
for example, everything after the first line of the Class definition was auto-indented during the paste.
export class MyClass extends Something<string> {
public blah: string = null;
constructor() { ... }
}
Just in case this may works for you as it did form me, i had this files
//server.ts
class Server{
...
}
exports.Server = Server
//app.ts
import {Server} from './server.ts'
And this actually raised an error but i changed server.ts to
//server.ts
export class Server{
...
}
and it worked 😎👌
Note: i am using this config
"target": "esnext",
"module": "commonjs",
I faced the same issue in a module that has no exports. I used it for side-effects only. This is what the TypeScript docs say about importing side-effects modules:
Though not recommended practice, some modules set up some global state that can be used by other modules. These modules may not have any exports, or the consumer is not interested in any of their exports. To import these modules, use:
import "./my-module.js";
In that situation, you can fix the "File is not a module" error by simply exporting an empty object:
// side-effects stuff
export default {};
I faced the same issue ("File is not a module error") for import js in vue component
import handleClientLoad from "../../../public/js/calendar.js"
I do this and solve it
// #ts-ignore
import handleClientLoad from "../../../public/js/calendar.js"
The file needs to add Component from core hence add the following import to the top
import { Component } from '#angular/core';
I got this module like this:
module MyModule {
export class Constants {
public static WIDTH:number = 100;
public static HEIGHT:number = 100;
....
}
}
export = MyModule;
Now I need to use MyModule.Constants.WIDTH in another class but I can't use import (I need to deliver this class js to a third party, and they don't use requirejs). Right now I use reference to get code checking but it keep giving this error (at transpilling time)
error TS2095: Could not find symbol 'MyModule'
What should I do now so I can use autocomplete and get rid of this error?
I hope you're not mindplay on the TypeScript forum otherwise I'm about to repeat myself.
export and import work together. You should either be using both or neither. If you check what the generated code looks like with and without the export keyword you'll see that export causes a module to be built. Since the third party can't use RequireJS I don't think this is what you want.
I would structure my classes like the following:
// file pkg/Foo.ts
module company.pkg {
export class Foo {}
}
// file pkg2/Bar.ts
module company.pkg2 {
export class Bar{}
}
Putting everything into the name space of your company minimizes the chance of a conflict with another library. Classes know about each other using a reference /// <reference path="..." /> which will allow it to compile.
Since you're not doing modules I would also compile to a single file using --out filename.js. That gets all the files included in (usually) the right order.