Ghost/ghost/admin/app/components/gh-canvas-header.js

import Component from '@ember/component';
import classic from 'ember-classic-decorator';
import {action} from '@ember/object';
import {run} from '@ember/runloop';
import {tagName} from '@ember-decorators/component';

@classic
@tagName('')
export default class GhCanvasHeader extends Component {
    @action
    initScrollWatch(element) {
        this._onScroll = run.bind(this, this.onScroll, element);
        this._scrollContainer = element.closest('.gh-main');
        if (this._scrollContainer) {
            this._scrollContainer.addEventListener('scroll', this._onScroll, {passive: true});
        }
    }

    @action
    clearScrollWatch() {
        if (this._scrollContainer) {
            this._scrollContainer.removeEventListener('scroll', this._onScroll);
        }
    }

    onScroll(element) {
        if (this._isSticky && this._scrollContainer.scrollTop < 10) {
            element.classList.remove('gh-canvas-header--sticky');
            this._isSticky = false;
        } else if (!this._isSticky && this._scrollContainer.scrollTop > 10) {
            element.classList.add('gh-canvas-header--sticky');
            this._isSticky = true;
        }
    }
}