Implementing a Custom Data Layer for First-Party and Business Data Collection

Created by Todd Belcher, Modified on Tue, 10 Sep at 5:24 PM by Todd Belcher

When collecting first-party data and/or business data, a custom data layer enables a truly tech-agnostic approach to proprietary data collection. The custom data layer may represent a core component of a data contract between site developers and marketing analysts.

Below is an example that accomplishes the following:

It establishes a proprietary data layer, called "layer1pd". That's the first thing you see in the code. A few variables are added to the data layer immediately, and others will be injected after it is established.
It categorizes pages-- this example is from a WordPress site-- using basic content site page types of home, page, section, and post.
It enables tracking of viewable page sections. Sections may be labeled with an attribute: data-viewable-section-name, and when that section is viewable it is added to a list of sections that were viewable during page engagement.
When blog posts are viewed, post tags are collected in a variable that can be utilized for reporting and personalization.

var layer1pd = {
    url: window.location.href,
    title: document.title,
    timestamp: Date.now(),
    viewableSections: [],
    // pageType and postTerms will be added later
};

function determinePageType() {
    const url = window.location;
    let pageType = 'page'; // Default to 'page'

    if (url.pathname === '/') {
        pageType = url.hash === '' ? 'home' : 'page';
    }

    if (document.querySelector('[data-viewable-section-name="section links"]')) {
        pageType = 'section';
    }

    if (document.querySelector('article')) {
        pageType = 'post';
    }

    return pageType;
}

function updateDataLayerWithViewableSection(sectionName) {
    if (!layer1pd.viewableSections.includes(sectionName)) {
        layer1pd.viewableSections.push(sectionName);
    }
}

function collectTerms() {
    if (layer1pd.pageType === 'post') {
        const termsListElement = document.querySelector('.elementor-post-info__terms-list');
        if (termsListElement) {
            const termsItems = termsListElement.querySelectorAll('.elementor-post-info__terms-list-item');
            const terms = Array.from(termsItems).map(item => item.innerText.trim());
            layer1pd.postTerms = terms;
        }
    }
}

function observeViewableSections() {
    let observer = new IntersectionObserver((entries, observer) => {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                let sectionName = entry.target.getAttribute('data-viewable-section-name');
                updateDataLayerWithViewableSection(sectionName);
            }
        });
    }, { threshold: 0.1 });

    document.querySelectorAll('[data-viewable-section-name]').forEach(element => {
        observer.observe(element);
    });

    document.querySelectorAll('[data-viewable-section-name]').forEach(element => {
        if (element.getBoundingClientRect().top < window.innerHeight && element.getBoundingClientRect().bottom >= 0) {
            updateDataLayerWithViewableSection(element.getAttribute('data-viewable-section-name'));
        }
    });
}

function initializeLayer1pd() {
    layer1pd.pageType = determinePageType();
    collectTerms();
    observeViewableSections();
}

if (document.readyState === 'complete') {
    initializeLayer1pd();
} else {
    window.addEventListener('DOMContentLoaded', initializeLayer1pd);
}