CODEWITHSUNDEEP
typescript
Chin
Chin

Reputation: 20665

Typescript initialize static variable of a class type

I have two classes Foo and Bar. In class Bar I have a static variable called myFoo and I want it to be automatically initialized:

class Foo {
}

class Bar {
    static myFoo: Foo = new Foo();
}

However, I'm getting this error:

Uncaught ReferenceError: Foo is not defined

If I initialize that static variable in Bar's constructor then it works fine:

class Bar {
    static myFoo: Foo;

    constructor() {
         Bar.myFoo = new Foo();
    }
}

Why is that? What did I do wrong when I tried to initialize the static variable myFoo directly?

Upvotes: 4

Views: 21466

Answers (4)

Karthik Sankar
Karthik Sankar

Reputation: 896

As Jeffery Grajkowski said, your second approach is incorrect. You could just initialize in definition.

class Bar {
  static myFoo: Foo = new Foo();
}

Upvotes: 0

Dave Cousineau
Dave Cousineau

Reputation: 13148

This requires JQuery, but is what I do to have the equivalent of a 'static constructor'.

namespace SomeNamespace {
   $(() => SomeClass.StaticConstructor());

   export class SomeClass {
      public static StaticConstructor() {
      }
   }
}

This is also useful as the "entry point" of your application, for example.

namespace SomeNamespace {
   $(() => SomeClass.Start());

   export class SomeClass {
      private static sInstance: SomeClass;

      public static Start() {
         SomeClass.sInstance = new SomeClass();
      }
   }
}

Upvotes: -1

Oded Breiner
Oded Breiner

Reputation: 29739

You can just have the call to initialize immediately follow the class declaration:

class MyClass {
    static initialize() {
        // Initialization
    }
}
MyClass.initialize();

Upvotes: 7

Jeffery Grajkowski
Jeffery Grajkowski

Reputation: 4061

You definitely don't want to do that second thing because that's going to overwrite myFoo every time you construct a new Bar and you certainly don't want that.

What you have here is a run time problem, not a compile time problem. The Foo class has to be loaded before the Bar class is loaded otherwise the static initializer will fail. If both classes are in a single file in the above order it works. If the classes are in separate files and you tell TypeScript to compile to a single file it should figure out the correct order for you (though there are bugs in that area). If you're compiling to separate files you'll need to include the scripts on the page in the correct order to satisfy the dependency.

Upvotes: 9

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