During a recent class, I defined an array with the type CustomType as shown below:
class Example {
public exampleArray: CustomType[];
public clearArray() {
this.exampleArray = [];
}
}
It appears that the clearArray method assigns an UNDEFINED type to an empty array, potentially causing loss of type information.
Is there a way to clear the array while still preserving its declared type?
The determination of type information relies on the field's type annotation (e.g., exampleArray: CustomType[]). Even though Javascript arrays are untyped at runtime, the compiler permits assigning an empty array ([]) to any variable as a safety measure. This is because, with no objects inside, it can be assumed to be an array of CustomType. Consequently, trying to push objects of a different type into the array will result in a compilation error due to the declared field type:
class CustomType { x: number}
class Example {
public exampleArray: CustomType[];
public clearArray() {
this.exampleArray = [];
this.exampleArray.push(new CustomType())
this.exampleArray.push({}) // error not a `CustomType`
}
}
Note:
If the variable had no type annotation, it would default to any[], which could lead to issues since type checking is not enforced when assigning or pushing elements to the array:
let noAnnotationArray = [] // any[]
In such cases, adding a type annotation is strongly recommended for ensuring type safety. Using type assertions (as proposed in other responses) might introduce unnoticed errors if non-matching items are added to the array later on:
let withAnnotation:CustomType[] = [{}] // error
let withAssertion = <CustomType[]>[{}] // no error even though we assign {}
It appears that this information is no longer current. A more up-to-date method exists.
this.customArray = [] as CustomType[];
Three possible methods for clearing an array:
Set the length of the array to 0
myArr.length = 0;
Utilize the splice method for Arrays
myArr.splice(0, myArr.length);
Use Pop() on each element of the array
while(myArr.length){
myArr.pop();
}
To completely empty a list, simply set the length property to 0
For example: this.arrayExample.length = 0
By setting the length to 0, you effectively remove all elements from the array while keeping the original reference intact.
Ensure the array is emptied, even when passed as a parameter in a method:
myArray.length = 0;
One potential solution is to test it out using
this.sampleArray = <CustomType[]>[];
I encountered an issue with searching multiple columns in my serverside datatables. Individual column searches work fine, but when trying to search on more than one column simultaneously, the filter does not function as expected. For example, searching by ...
I've been struggling with this issue for quite some time now and I can't seem to figure it out, no matter how hard I try. It seems that my input field is not capturing the value entered by the user for some unknown reason. Let me share the code ...
I'm trying to implement the npm package ng2-canvas-whiteboard into my Ionic 3 app. I followed all the instructions on the npm page and here is my package.json: "dependencies": { "@angular/common": "4.0.2", "@angular/compiler": "4.0.2", ...
I am in the process of building a website that incorporates SVG technology. My issue is with some SVG icons that have animated effects when scrolling, but the animation triggers as soon as they come into view. What I really need is for these icons to sta ...
I have a web application dashboard with a common header across all HTML files, including the profile page, page 1, and SignIn. However, I want the SignIn page to be different without the common header. How can I redirect to signin.html without using ng-vie ...
I'm currently working on a directive that needs to reload its content automatically. Unfortunately, I haven't had much success with it so far. Any assistance would be greatly appreciated. UPDATE: I attempted the suggested solution but encountere ...
I am faced with a nested JSON array structure like this: Parent: { Child1: [ {name:'grandchild1', value:'abc', checked:true}, {name:'grandchild2', value:'pqr', checked:false} ], Ch ...
Is there a way to automatically run VSCode's 'Organize Imports' quickfix on every file in a project, similar to how tslint can be run programatically over the entire project? tslint --project tsconfig.json --config tslint.json --fix I want ...
Below is the current code snippet: HTML <center><li ng-repeat = "x in items | orderBy: 'priority'"> <!-- color code priorities --> <span ng-style="cmplt" ng-class="{ red: x.type == &apo ...
When I click on one of the two links, it displays a different image. The first time works fine, but if I click again on the same link, the image is correct but the hover effect moves to the other link, making it appear as if the second link is selected ins ...
I need help setting page1.html to display by default when the page loads. Can you provide some guidance? Appreciate your assistance in advance. <head> <title>Test</title> <meta http-equiv="content-type" content="tex ...
My HTML file contains: <!Doctype HTML> <html> <head> <title>Orange’s Game</title> <meta charset="utf-8"> <script src="game.js”></script> </head> <body> <input type="button ...
After configuring a set of operations in the UI and initiating the operation, a Python script is called in the backend. It is necessary to display the logs generated by the Python script on the UI. I managed to implement this in a similar way as described ...
I have a React application where I am displaying an image (an SVG) and I want the user to be able to download it by clicking on a button. The image is stored in Firebase Storage. However, I am encountering an issue with CORS error: Access to fetch at &ap ...
I am interested in enhancing the appearance of an Ionic 2 range element by adding labels throughout, similar to a progress bar. While I have successfully added labels at the beginning and end, I would like to explore placing labels dynamically on either si ...
One of the key elements of this website is the implementation of iframes, with only one displayed at a time. However, my current issue revolves around the inability to scroll within these iframes due to their absolute positioning. I have attempted variou ...
I am currently working on a web application using three.js with Angular and facing some challenges when trying to set the precise positions of objects. The requirement is to load various objects and position them in specific locations. In order to load di ...
I have successfully constructed a Mapbox map with a complex custom popup structure, complete with photos and formatting. The data is being fed from a .csv file using omnivore, and the popups are being created on ready. Additionally, I have implemented a se ...
I tried incorporating the bootstrap-star rating v4.1.0 from here, but unfortunately, it's not functioning as expected in my project. In my index.html file, I have included the following libraries: <!DOCTYPE html> <html lang="en"> ...
As part of my project, I am designing an admin panel for a distribution company. They have specifically requested a feature where they can input orders for all clients through a single page. To meet this requirement, I have created a dynamic form that gene ...