While it is commonly understood that the compiler performs static type checking, I am curious about the specific methods it employs to ensure that nullable types are not inadvertently used.
While it is commonly understood that the compiler performs static type checking, I am curious about the specific methods it employs to ensure that nullable types are not inadvertently used.
The concept of nullability/undefinedness checking involves a shift in how the type system conceptualizes types. This process occurs during typechecking and does not result in any runtime enforcement through emitted JavaScript code.
Essentially, a type can be viewed as a set of values. For instance, the set of values for the boolean type typically consists of only two values: true and false. On the other hand, the string type encompasses an unlimited number of strings such as "hello", "world", and various other strings.
TypeScript validates that when a value is used within a certain type context, it belongs to the defined set of values for that type. For example, since true is not part of the domain of numbers, attempting to use true where a number is expected is considered invalid.
In TypeScript without strict null checking, null and undefined are considered to be part of every type's domain. Therefore, the boolean type actually includes four values: true, false, undefined, and null. However, this can lead to issues because undefined and null do not behave identically to true and false. Particularly for entities with properties and methods, like the substr method within the string domain, it can become cumbersome due to its absence in null and undefined.
With the implementation of strict null checking in TypeScript, null and undefined are categorized into their respective types instead of being included in all domains. Consequently, null cannot be utilized in contexts where a string is expected anymore, as it no longer falls within the bounds of the string domain. The updated type string | null now signifies a value that could either belong to the string set or be the distinct value null.
This explanation has been inspired by Anders Hejlsberg's presentation at Build 2016, starting around 44:30. Undoubtedly, his elucidation may provide a more thorough understanding, especially with the help of accompanying visual aids.
While TypeScript offers static typing, it is important to note that this typing is only enforced during compilation and can be bypassed when the code is transpiled into JavaScript. For example:
let bar: { anotherProperty: string } = { anotherProperty: "h" }; // anotherProperty is defined as a non-nullable string
bar["anotherProperty"] = null; // circumventing type validation!
My task involves parsing a string with values like ABC000012005,ABC0000012005. The desired output is to extract the prefix and numbers without leading zeros, formatted as ABC 12005, ABC 12005 ...
I have successfully implemented an API that is providing the desired response. However, I am now looking to set this response directly into the body section. Currently, the response is being displayed within a <pre> tag on the website as shown below ...
While working with Angular 8, I am attempting to utilize abstract components. My goal is to define the templateUrl and styleUrls in my abstract class, but have the selector name specified in the implemented class. Here is an example: @Component({ // sel ...
For my e-commerce project, I am looking to utilize the Google Maps API to input the location of a user's shop. I have successfully utilized Google Cloud Functions to insert the latitude, longitude, and address data. Currently, the data can be insert ...
I'm working on implementing a show/hide functionality using a switch. I want the component to be displayed when the switch is turned on and hidden when it's turned off. Here's the code I've written: const VirtualEventSection = ({ con ...
Recently, I've been diving into the bluebird promises library. To practice using it, I set up a basic express app with just one file and one route - a GET request to /test. The scenario I'm working on involves a promise with an interval that res ...
I am attempting to create a volume meter, using the web audio API to create a pulsation effect with a sound file loaded in an <audio> element. The indicator effect is working well with this code; I am able to track volume changes from the playing aud ...
I've been developing with Angular 7, trying to display a <div> ... </div> based on multiple values that I declared as : Boolean = false; in the .ts file. These values are updated in ngOnInit, but for some reason, the page keeps redirecting ...
I am currently in the process of setting up a basic template for my demonstration project and writing my first node.js program. The piece of code below is functioning properly for my initial test, but it contains duplicated sections - Getting connection, E ...
Hi there, can someone help me figure out how to save changes to the value attribute of an HTML input tag that is being incremented by JavaScript? Currently, every time I click on a specific element, the input field should increase by one. The problem is th ...
There are two separate html pages named home and about. Each page contains a js variable defined at the top of the page: var pageAlias = 'home'; // on the home page var pageAlias = 'about'; // on the about page The goal is to pass thi ...
Currently, I have a script set up to display a map with two markers. Whenever I hover over one of the markers, a popup tooltip appears with location information. My question is, how can I make the information appear by default without needing to hover ov ...
My HTML5 video app includes a combination of video, a JavaScript swipable playlist, and other animated overlays. When using the app on iOS, the performance of playlist swiping and overlay animations is great upon initial load. However, after playing a vid ...
I need assistance with splitting a string by a specific character, such as a '/'. However, I also require the characters directly preceding the split character up to the space before them to be included in the result. For instance: let myStr = ...
Currently, I use two enums as shown: enum Tab { Approved = "Approved", Pending = "Pending", Sold = "Sold", } enum ProductStatus { Approved = "Approved", Pending = "Pending", Sold = "Sold&q ...
Currently, I have a line of code that dynamically sets the default selection of a selection box in html using jQuery. var y=...a value from the DB; this.$(".status option[value=y]").attr("selected", "selected"); The issue is that it only works if I ...
When the client reconnects after a network drop, the disconnect event is triggered on the server. Client code: var url ='192.168.1.101', port = '80', socket = io.connect('http://' + url + ':' + port, { &apo ...
In my current project, I have successfully implemented an IDL for passing a string value from JavaScript to C++. The JavaScript code effectively passes a string value to the C++/COM object. [id(1), helpstring("method DoSomething")] HRESULT DoSomething([in ...
Hey there, I've been using the Datatable plugin and it's really great. However, I've come across a problem with complex headers like this: <thead> <tr><td>some text</td></tr> <tr><td>some te ...
Currently, I am tackling a basic For/in loop exercise as part of a course curriculum I am enrolled in. The exercise involves working with a simple object containing 3 properties and creating a function that takes two parameters - the object name and the it ...