javascript - Angular 4 how to use innerHtml with *ngFor?

Javascript - Angular 4 how to use innerHtml with *ngFor?

In Angular (including Angular 4), using innerHTML with *ngFor can be a bit tricky because Angular sanitizes and protects against XSS (Cross-Site Scripting) attacks by default. However, there are ways to safely render HTML content dynamically within an *ngFor loop. Here's how you can approach it:

Using innerHTML with *ngFor in Angular 4

  1. HTML Sanitization and DomSanitizer: Angular sanitizes HTML content by default to prevent XSS vulnerabilities. To use innerHTML safely, you need to bypass Angular's built-in security.

  2. Import DomSanitizer: Angular provides DomSanitizer service to safely sanitize and bypass security for specific HTML content.

  3. Safe HTML Rendering: Use DomSanitizer to mark HTML content as safe before binding it to innerHTML.

Example:

Assume you have an array of strings containing HTML content that you want to render using *ngFor and innerHTML. Here's how you can do it:

Template (component.html):

<div *ngFor="let htmlContent of htmlContents"> <div [innerHTML]="sanitizeHtml(htmlContent)"></div> </div>

Component (component.ts):

import { Component } from '@angular/core'; import { DomSanitizer, SafeHtml } from '@angular/platform-browser'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { htmlContents: string[] = [ '<p>This is <strong>HTML</strong> content 1.</p>', '<p>This is <em>HTML</em> content 2.</p>', '<p>This is <span style="color: red;">HTML</span> content 3.</p>' ]; constructor(private sanitizer: DomSanitizer) {} sanitizeHtml(html: string): SafeHtml { return this.sanitizer.bypassSecurityTrustHtml(html); } }

Explanation:

  • Template: Use *ngFor to iterate over htmlContents array, which contains HTML strings. Bind each htmlContent to [innerHTML] directive.

  • Component:

    • Import DomSanitizer and SafeHtml from @angular/platform-browser.
    • Define an array htmlContents containing HTML strings.
    • Create a method sanitizeHtml that uses DomSanitizer to mark HTML content as safe (bypassSecurityTrustHtml). This ensures Angular does not sanitize the HTML content and allows it to be rendered safely.

  • Security Note: Always ensure that the HTML content you are rendering using innerHTML is trusted and does not come from untrusted sources to prevent XSS attacks.

Important Points:

  • Sanitization: Angular sanitizes HTML by default to prevent XSS vulnerabilities. Use DomSanitizer to mark HTML as safe before binding it to innerHTML.

  • Performance: Rendering HTML with innerHTML can affect performance, especially when rendering large amounts of content. Use it judiciously.

By following these steps, you can safely use innerHTML with *ngFor in Angular 4 to render dynamic HTML content within your application. This approach ensures both security and flexibility in handling HTML content dynamically.

Examples

  1. *Angular 4 ngFor innerHtml Example

    Description: How to bind HTML content dynamically using *ngFor in Angular 4.

    Code:

    <div *ngFor="let item of items"> <div [innerHtml]="item.htmlContent"></div> </div>

    Explanation: This code iterates over items array in Angular template using *ngFor and binds each item's htmlContent property to innerHtml of a div.

  2. *Angular 4 sanitize HTML with DomSanitizer and ngFor

    Description: How to sanitize HTML content when using innerHtml with *ngFor in Angular 4.

    Code:

    import { DomSanitizer } from '@angular/platform-browser'; constructor(private sanitizer: DomSanitizer) {} sanitizeHtml(html: string) { return this.sanitizer.bypassSecurityTrustHtml(html); }

    Explanation: Use DomSanitizer to safely bind HTML content to innerHtml in Angular, ensuring security against XSS vulnerabilities.

  3. *Angular 4 bind HTML string with ngFor

    Description: How to bind a string of HTML content using *ngFor in Angular 4.

    Code:

    export class AppComponent { items: string[] = ['<p>Paragraph 1</p>', '<p>Paragraph 2</p>']; } 
    <div *ngFor="let item of items" [innerHtml]="item"></div>

    Explanation: This example shows how to directly bind HTML strings stored in an array to innerHtml using *ngFor directive in Angular.

  4. Angular 4 bypassSecurityTrustHtml with innerHtml

    Description: How to use bypassSecurityTrustHtml method to bind HTML content with innerHtml in Angular 4.

    Code:

    import { DomSanitizer } from '@angular/platform-browser'; constructor(private sanitizer: DomSanitizer) {} sanitizeHtml(html: string) { return this.sanitizer.bypassSecurityTrustHtml(html); } 
    <div *ngFor="let item of items" [innerHtml]="sanitizeHtml(item.htmlContent)"></div>

    Explanation: Use DomSanitizer to safely bind HTML content to innerHtml in Angular, ensuring security by bypassing Angular's default sanitization.

  5. *Angular 4 nested ngFor with innerHtml

    Description: How to use nested *ngFor with innerHtml in Angular 4 to iterate and bind HTML content.

    Code:

    <div *ngFor="let group of groups"> <div *ngFor="let item of group.items" [innerHtml]="item.htmlContent"></div> </div>

    Explanation: This code demonstrates nesting *ngFor directives to iterate through nested arrays (groups and items) and bind HTML content to innerHtml.

  6. Angular 4 innerHtml binding and trackBy

    Description: How to optimize performance when using innerHtml with *ngFor in Angular 4 by using trackBy.

    Code:

    trackByFn(index: number, item: any) { return item.id; // Unique identifier for each item } 
    <div *ngFor="let item of items; trackBy: trackByFn" [innerHtml]="item.htmlContent"></div>

    Explanation: Implement a trackBy function to improve Angular's rendering performance when iterating over items with innerHtml binding in *ngFor.

  7. Angular 4 bind HTML content conditionally

    Description: How to conditionally bind HTML content using innerHtml with *ngFor in Angular 4.

    Code:

    <div *ngFor="let item of items" [innerHtml]="item.showHtml ? item.htmlContent : ''"></div>

    Explanation: This example demonstrates binding HTML content conditionally based on a boolean flag (showHtml) using innerHtml with *ngFor.

  8. Angular 4 bind HTML content from JSON

    Description: How to bind HTML content fetched from JSON using innerHtml with *ngFor in Angular 4.

    Code:

    items: any[] = [ { htmlContent: '<p>Paragraph 1</p>' }, { htmlContent: '<p>Paragraph 2</p>' } ]; 
    <div *ngFor="let item of items" [innerHtml]="item.htmlContent"></div>

    Explanation: In this scenario, items array contains objects with htmlContent properties, which are bound to innerHtml in Angular template using *ngFor.

  9. Angular 4 innerHtml binding security

    Description: How to handle security concerns when using innerHtml binding in Angular 4.

    Code:

    <div *ngFor="let item of items" [innerHtml]="sanitizeHtml(item.htmlContent)"></div>

    Explanation: Use DomSanitizer's bypassSecurityTrustHtml method (as shown previously) to ensure safe binding of HTML content to innerHtml in Angular.

  10. Angular 4 innerHtml binding in component

    Description: How to bind HTML content to innerHtml directly within an Angular component in Angular 4.

    Code:

    @Component({ selector: 'app-my-component', template: `<div *ngFor="let item of items" [innerHtml]="item.htmlContent"></div>` }) export class MyComponent { items: any[] = [ { htmlContent: '<p>Paragraph 1</p>' }, { htmlContent: '<p>Paragraph 2</p>' } ]; }

    Explanation: Define items array in the component class and bind HTML content to innerHtml within the component's template using *ngFor directive in Angular 4.

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