A script to hide English words/sentences in front-side cards. (works on Anki 2.1on Windows , AnkiDroid 2.9)

card.html

<script>
(function () {
    const IGNORED_TAGS = ["SCRIPT", "STYLE"];

    // List all text nodes under the target elements
    const nodes = [];
    Array
        .from(document.getElementsByClassName('ja'))
        .forEach(function (root) {
            const treeWalker = document.createTreeWalker(root, NodeFilter.SHOW_TEXT, null, false);
            let node;
            while (node = treeWalker.nextNode()) {
                if (!IGNORED_TAGS.includes(node.parentNode.tagName.toUpperCase())) {
                    nodes.push(node);
                }
            }
        });

    // Mark English sentence/words as class="en"
    nodes.forEach(function (node) {
        const html = node.textContent.replace(/([a-zA-Z]([a-zA-Z' .,-]*[a-zA-Z'.])?)/g, '<span class="en">$1</span>');
        const p = document.createElement('p');
        p.innerHTML = html;
        Array.from(p.childNodes).forEach(function (e, idx) {
            // this changes p.childNodes' parentNode and affects forEach()
            node.parentNode.insertBefore(e, node);
        });
        node.parentNode.removeChild(node);
    });

}());
</script>
</div>