@syntronic/ngx-highlight

Angular directives for highlighting search matches in text, built on the native CSS Custom Highlight API. No DOM mutation, no wrapping matched text in <mark> elements — ranges are painted directly by the browser.

• Works across nested text nodes and multiple elements.
• Supports a single group-wide search term, or several independent named searches within one group (e.g. per-column filters in a table).
• Zoneless-friendly: built entirely on Angular signals (input(), contentChildren(), afterRenderEffect()).

Requirements

• Angular ^22.0.0
• A browser with CSS.highlights support (Chromium, Safari; Firefox behind a flag as of writing). The directives no-op silently when unsupported.

Installation

npm install @syntronic/ngx-highlight

Usage

Basic: single search term

Wrap the searchable area with ngxHighlightGroup, pass it a unique highlight name and the current search term, then mark each searchable element with ngxHighlightTarget.

import { Component, signal } from '@angular/core';
import { HighlightGroupDirective, HighlightTargetDirective } from '@syntronic/ngx-highlight';

@Component({
  selector: 'app-example',
  imports: [HighlightGroupDirective, HighlightTargetDirective],
  template: `
    <input [value]="searchTerm()" (input)="searchTerm.set($event.target.value)" />

    <ul [ngxHighlightGroup]="'device-list'" [highlightSearchTerm]="searchTerm()">
      @for (device of devices; track device.id) {
        <li ngxHighlightTarget>{{ device.name }}</li>
      }
    </ul>
  `,
})
export class ExampleComponent {
  readonly searchTerm = signal('');
  readonly devices = [
    { id: 1, name: 'Water meter A1' },
    { id: 2, name: 'Water meter B2' },
  ];
}

Style the highlight with the ::highlight() pseudo-element, using the same name passed to ngxHighlightGroup:

::highlight(device-list) {
  background-color: yellow;
  color: black;
}

Minimum match length

Avoid highlighting on very short, noisy terms with highlightMinLength (default 1):

<div [ngxHighlightGroup]="'device-list'" [highlightSearchTerm]="searchTerm()" [highlightMinLength]="3">
  <span ngxHighlightTarget>{{ device.name }}</span>
</div>

With highlightMinLength="3", a search term of "he" produces no highlight; "hel" does.

Named searches: independent terms per column

When a table (or any layout) needs a different search term per column, register each one with ngxHighlightSearch and pair it with a matching ngxHighlightTarget name. Unnamed targets keep matching the group-level highlightSearchTerm as before.

<table [ngxHighlightGroup]="'device-table'">
  <thead>
    <tr>
      <th>
        <input ngxHighlightSearch="name" [highlightSearchTerm]="nameFilter()" (input)="nameFilter.set($event.target.value)" />
      </th>
      <th>
        <input ngxHighlightSearch="location" [highlightSearchTerm]="locationFilter()" (input)="locationFilter.set($event.target.value)" />
      </th>
    </tr>
  </thead>
  <tbody>
    @for (device of devices; track device.id) {
      <tr>
        <td [ngxHighlightTarget]="'name'">{{ device.name }}</td>
        <td [ngxHighlightTarget]="'location'">{{ device.location }}</td>
      </tr>
    }
  </tbody>
</table>

A named search unregisters itself automatically when its term becomes empty/null/undefined, or when the directive is destroyed.

API

HighlightGroupDirective ([ngxHighlightGroup])

Input	Alias	Type	Default	Description
highlightName	ngxHighlightGroup	string (required)	—	The name registered in CSS.highlights — pair with ::highlight(name).
highlightSearchTerm	—	string	''	Group-wide search term applied to unnamed targets.
highlightMinLength	—	number	1	Minimum term length (after trim) before any highlighting occurs.

HighlightTargetDirective ([ngxHighlightTarget])

Input	Alias	Type	Default	Description
highlightSearchTargetName	ngxHighlightTarget	string	''	When set, only matches the named search registered under the same name.

HighlightSearchDirective ([ngxHighlightSearch])

Input	Alias	Type	Default	Description
highlightSearchName	ngxHighlightSearch	string (required)	—	Name shared with the matching ngxHighlightTarget.
highlightSearchTerm	—	string | null | undefined (required)	—	The term for this named search.

Development

This repository is an Angular CLI workspace containing a single library project (projects/ngx-highlight).

npm install
npm run build   # ng build ngx-highlight -> dist/ngx-highlight
npm run test    # ng test ngx-highlight (Vitest + real Chromium via vitest-browser-angular)
npm run lint    # ng lint ngx-highlight

Tests run against real Chromium (not jsdom) because they assert against the live CSS.highlights registry, which jsdom does not implement.

Publishing

npm run build
cd dist/ngx-highlight
npm publish

License

MIT