Kristiyan Kostadinov
68017d4e75
According to the HTML specification most attributes are defined as strings, however some can be interpreted as different types like booleans or numbers. [In the HTML standard](https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#boolean-attributes), boolean attributes are considered `true` if they are present on a DOM node and `false` if they are omitted. Common examples of boolean attributes are `disabled` on interactive elements like `<button>` or `checked` on `<input type="checkbox">`. Another example of an attribute that is defined as a string, but interpreted as a different type is the `value` attribute of `<input type="number">` which logs a warning and ignores the value if it can't be parsed as a number. Historically, authoring Angular inputs that match the native behavior in a type-safe way has been difficult for developers, because Angular interprets all static attributes as strings. While some recent TypeScript versions made this easier by allowing setters and getters to have different types, supporting this pattern still requires a lot of boilerplate and additional properties to be declared. For example, currently developers have to write something like this to have a `disabled` input that behaves like the native one: ```typescript import {Directive, Input} from '@angular/core'; @Directive({selector: 'mat-checkbox'}) export class MatCheckbox { @Input() get disabled() { return this._disabled; } set disabled(value: any) { this._disabled = typeof value === 'boolean' ? value : (value != null && value !== 'false'); } private _disabled = false; } ``` This feature aims to address the issue by introducing a `transform` property on inputs. If an input has a `transform` function, any values set through the template will be passed through the function before being assigned to the directive instance. The example from above can be rewritten to the following: ```typescript import {Directive, Input, booleanAttribute} from '@angular/core'; @Directive({selector: 'mat-checkbox'}) export class MatCheckbox { @Input({transform: booleanAttribute}) disabled: boolean = false; } ``` These changes also add the `booleanAttribute` and `numberAttribute` utilities to `@angular/core` since they're common enough to be useful for most projects. Fixes #8968. Fixes #14761. PR Close #50420
Angular - The modern web developer's platform
Angular is a development platform for building mobile and desktop web applications
using TypeScript/JavaScript and other languages.
Contributing Guidelines
·
Submit an Issue
·
Blog
Documentation
Get started with Angular, learn the fundamentals and explore advanced topics on our documentation website.
Advanced
Development Setup
Prerequisites
- Install Node.js which includes Node Package Manager
Setting Up a Project
Install the Angular CLI globally:
npm install -g @angular/cli
Create workspace:
ng new [PROJECT NAME]
Run the application:
cd [PROJECT NAME]
ng serve
Angular is cross-platform, fast, scalable, has incredible tooling, and is loved by millions.
Quickstart
Ecosystem
Changelog
Learn about the latest improvements.
Upgrading
Check out our upgrade guide to find out the best way to upgrade your project.
Contributing
Contributing Guidelines
Read through our contributing guidelines to learn about our submission process, coding rules, and more.
Want to Help?
Want to report a bug, contribute some code, or improve the documentation? Excellent! Read up on our guidelines for contributing and then check out one of our issues labeled as help wanted or good first issue.
Code of Conduct
Help us keep Angular open and inclusive. Please read and follow our Code of Conduct.
Community
Join the conversation and help the community.
Love Angular? Give our repo a star ⭐ ⬆️.