声明前使用的“ Bar”类

Question

I have a class named Bar :

class Bar {
  private readonly foo: string;
  constructor() {
    this.foo = "foo";
  }
}

And in my main file I'm trying to use it like this:

const bar: Bar = new Bar();

But this line gives me the error:

Class 'Bar' used before its declaration.

I can make it a var and declare it inside a function but I'm looking for a better solution which allows me to declare the bar as a constant.

The problem is Typescript compiling the project into a single Javascript file which declares the class after the attempted use.

Altough @Fenton's solution works fine. There is another:

Inside tsconfig.json you can type:

"files": [
    "libs/Bar.ts",
],
"include": [
    "**/*"
]

This will tell Typescript to compile libs/Bar.ts before the others.

Answer 1

You may need to hint to the compiler that the other file is there, although this depends on your IDE as some work this out for themselves.

///<reference path="./libs/Bar.ts" />

const bar: Bar = new Bar();

Notes on Comments

This is so ugly... - Jonas W.

My opinion has long been that you should prefer modules, and module loaders over namespaces, and reference comments . It has been my opinion since before they were called this , but bear in mind the OP has already made this comment.

I don't use export or import because the output is a single file targeting es5

Now it is in fact still possible to achieve a single file output, targeting ES5, even if you write modules with imports, because you can use additional tooling to process the modules into a single file, or you can use a module loader like SystemJS or RequireJS - but we ought to consider how much subjectivity we ought to introduce to an answer; and how appropriate it may be to attempt to convert every person with a question to our own workflow.

For example, I disagree with bundling an entire program into a single script file*, when it could be better delivered by leaving the modules intact - but I don't try to answer every webpack question with that.

* I disagree to the extent that bundling is currently heralded as being a "best practice", based on dated premises.