Recognizing TypeScript's Jurisdictional Boundary

Angular 2 , TypeScript 1 Comment »

While I was exploring the current Angular 2 documentation regarding forms and form field validity, I caught myself wondering why the Angular code wouldn't block or complain about an attempt to assign an incorrect data type value to an object property.  Given the following TypeScript object:


export class Villain {
  id: number;
  name: string;
  age: number;
  dateOfBirth: Date;
}

...you could be forgiven if you thought, for a brief moment at least, that a user entering property values for a Villain via a form would experience an error of some kind if they tried to enter a non-number in the age form field,or a string value of "7/14/84" in the date of birth field.

But of course that wouldn't happen. TypeScript only enforces those types when it compiles the code, preventing programmers from using the wrong data type in the code. That type enforcement is not carried through to the resulting JavaScript.

This is hardly a revelation.  TypeScript is a tool for writing JavaScript: it doesn't alter the base behavior or functionality of JavaScript.  But I can see developers spending a few hours coding classes and service methods in TypeScript, then turning their attention to the code that interacts with the web UI and having to remind themselves that the type protection doesn't apply to user/UI actions that change the class property values.  In that area of the code, you have to enforce the data types with explicit code.

And it made me wonder if there should be a way to carry those data type restrictions on class properties down to the resulting JavaScript code by default.  Not sure how feasible that would be.  I would think you'd have to make each property a private property with getter/setter methods where the setter method would ensure the incoming value met the data type criteria.  But then how would a data type mistmatch be handled?  You probably wouldn't want to throw an error:  you'd want to record the attempt in some readable property.  Would you prevent the property from being set to an invalid value, or would you allow it and count on the developer to write code to inspect the object for validity issues before proceeding?  And how would you provide a mechanism for adding custom validations on top of the data type validations?

No matter how you went about it, you'd end up with an opinionated process for enforcing the data types that probably wouldn't work for everyone, which is probably why TypeScript doesn't do anything like that with the compiled JavaScript code.

Learning Angular 2: Exploring the Current Features of Forms

Angular 2 , Angular 2 Learning No Comments »

One of the things I noticed when I completed the official "Tour of Heroes" Angular 2 tutorial was that there wasn't a lesson on using forms:  in Angular 1 input bindings that were managed under ngForm provided data state, validation, and error-handling features, and I had heard that Angular 2 had the same thing.

Apparently forms are another aspect of Angular 2 that is still somewhat of a moving target: the current "Forms" chapter under the "Basics" category of the Angular 2 site documents a deprecated version and points to a newer documentation page.  I decided to read through the newer documentation page and try out the current forms functionality myself, building off of my existing Tour of Heroes project codebase.

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Learning Angular 2: Tour of Heroes Tutorial, Lesson 7

Angular 2 , Angular 2 Learning No Comments »

The final lesson of the Tour of Heroes tutorial covers using Angular 2 with HTTP.

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Learning Angular 2: Tour of Heroes Tutorial, Lesson 6

Angular 2 , Angular 2 Learning , IntelliJ IDE No Comments »

The next lesson in the Tour of Heroes tutorial covers an important topic: routing.  I've been looking forward to this particular lesson because I was curious as to how routing would work given the new component-structured architecture.

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Learning Angular 2: Tour of Heroes Tutorial, Lesson 5

Angular 2 , Angular 2 Learning No Comments »

Lesson 5 of the Tour of Heroes tutorial introduces services.

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