How to format and highlight xml string in js? (with code)

/**
 * 格式化xml
 * @param content
 * @returns {*}
 */
this.parse_xml = function(content) {
    let xml_doc = null;
    try {
        xml_doc = (new DOMParser()).parseFromString(content.replace(/[\n\r]/g, ""), 'text/xml');
    } catch (e) {
        return false;
    }

    function build_xml(index, list, element) {
        let t = [];
        for (let i = 0; i < index; i++) {
            t.push(&#39;    &#39;);
        }
        t = t.join("");
        list.push(t + &#39;&lt;<span class="code-key">&#39;+ element.nodeName +&#39;</span>&gt;\n&#39;);
        for (let i = 0; i < element.childNodes.length; i++) {
            let nodeName = element.childNodes[i].nodeName;
            if (element.childNodes[i].childNodes.length === 1) {
                let value = element.childNodes[i].childNodes[0].nodeValue;
                let value_color = !isNaN(Number(value)) ? &#39;code-number&#39; : &#39;code-string&#39;;
                let value_txt = &#39;<span class="&#39;+ value_color +&#39;">&#39; + value + &#39;</span>&#39;;
                let item = t + &#39;    &lt;<span class="code-key">&#39; + nodeName +
                    &#39;</span>&gt;&#39; + value_txt + &#39;&lt;/<span class="code-key">&#39; + nodeName + &#39;</span>&gt;\n&#39;;
                list.push(item);
            } else {
                build_xml(++index, list, element.childNodes[i]);
            }
        }
        list.push(t + &#39;&lt;/<span class="code-key">&#39;+ element.nodeName +&#39;</span>&gt;\n&#39;);
    }

    let list = [];
    build_xml(0, list, xml_doc.documentElement);

    return list.join("");
};

.code-string{color:#993300;}
.code-number{color:#cc00cc;}
.code-boolean{color:#000033;}
.code-null{color:magenta;}
.code-key{color:#003377;font-weight:bold;}