In JS, there's no way to assert that a property is definitely assigned

Keywords: JSDoc, Salsa, JavaScript, definite, initialization, initialized, assigned, assertion

class ElementWrapper {
  constructor() {
    this.init();
  }

  init() {
    this.element = document.createElement('div');
  }

  getElementStyle() {
    this.element.style // error: element is possibly undefined
  }
}

We need a way to convince TypeScript in strictNullChecks that this.element is initialized in getElementStyle. Basically a definite initialization assertion.

Related is #23405 which tracks non-null assertions on the expression level.