Angular error TS2339: The property 'before' is not found on type 'HTMLElement' / 'HTMLTextAreaElement' / etc

Objective: My goal is to reposition a div (containing a mat-select dropdown) ABOVE a mat-card-title when the user is accessing the site from a mobile device. If the user is not on a mobile device, the div should remain in its original position to the right of the mat-card-title.

Appearance on non-mobile devices: https://i.sstatic.net/RMPEa.png

Approaches Tried:

  • I attempted to use ngIf conditions above and below the div, but found it cluttered the HTML structure.
  • I considered media queries but realized they typically involve elements moving down rather than up, especially when nested.
  • Following a Stack Overflow article on JavaScript manipulation of DOM elements, I experimented with vanilla JavaScript.
  • While jQuery solutions were also explored, I ultimately decided against using jQuery for this project.

Challenge: I encountered TS2339 error regarding the 'before' property not existing on type 'HTMLElement' or 'HTMLTextAreaElement'.

Despite attempting various variable casts as suggested in a similar Stack Overflow thread, the issue remains unresolved.

Seeking guidance on potential next steps.

HTML Snippet:

<div class="title-container">
    <mat-card-title id="signInTitle" class="text-center" i18n="@@MoVeSeLo_H1_1">
        Please Sign In
    </mat-card-title>
    <div id="langDropDown">
        <div *ngIf="(_lang_switch_controls)">
            <form [formGroup]="_siteForm">
                <mat-form-field class="language-field" appearance="outline">
                    <mat-select (selectionChange)="changeSite($event)" [value]="languages[i].value">
                        <mat-option *ngFor="let language of languages" [value]="language.value">
                            {{language.viewValue}}
                        </mat-option>
                    </mat-select>
                </mat-form-field>
            </form>
        </div>
    </div>
</div>

TypeScript Snippet:

const signInTitle = <HTMLTextAreaElement>document.getElementById("signInTitle");
const langDropDown = <HTMLDivElement>document.getElementById("langDropDown");

var uagent = navigator.userAgent.toLowerCase();
if (uagent.match(/iPad|iPhone|android/)) {
    signInTitle.before(langDropDown);
}

Answer №1

HtmlElement and similar elements are specified in the TypeScript DOM library.

To successfully implement the ChildNode interface (which includes the before method) for these elements, you must have at least TypeScript 3.1.1 installed.

If updating TypeScript is not an option, you can utilize the insertBefore method or utilize the Renderer2 service from Angular to manipulate DOM elements.

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