Since version 4.7, TypeScript fully supports ECMAScript class static blocks, so the workaround syntax using a private static field with an "immediately evaluated function" (IEF) can now be simplified.

Before:

class Foo {
  static #static = (() => {
    console.log("Foo is being initialized!");
  })();
}

After:

class Foo {
  static {
    console.log("Foo is being initialized!");
  }
}

In Ext JS, it is often required to use this in the constructor before calling super() . According to ECMAScript and thus TypeScript class semantics, this is not allowed and results in an error. To still be able to use TypeScript classes for Ext JS development, we found a workaround described in the following. Assume there is a class Bar with a constructor that takes a string and a boolean, an Ext JS subclass could look like so:

class Foo extends Bar {
  #field: string;
  constructor(a: string) {
    super(...(() => {
      /* all code accessing 'this' before 'super()': */
      this.#field = a;
      // super args must be returned and spread ('...'):
      return [a + "!", this.#compute()];
    )());
    /* code after super call: */
    console.log(this.#field);
  }
  #compute(): boolean { ... }
}

The pattern is slightly simpler when there is just one super call parameter, but is still hardly comprehensible and cumbersome to write.

The new workaround that reads and writes simpler is to define an alias for this and use @ts-expect-error to ignore the resulting error exactly in that line. The new syntax for the code above looks like so:

class Foo extends Bar {
  #field: string;
  constructor(a: string) {
    // @ts-expect-error Ext JS semantics
    const this$ = this;
    // same code as inside the IEF with every 'this' is replaced by 'this$':
    this$.#field = a;
    // normal super call:
    super(a + "!", this$.#compute());
    /* code after super call: */
    console.log(this.#field);
  }
  #compute(): boolean { ... }
}