contentScript.js

// Helper functions
function getElementsByClassName(node, classname) {
    if (node.getElementsByClassName) { // use native implementation if available
        return node.getElementsByClassName(classname);
    } else {
        return (function getElementsByClass(searchClass, node) {
            if (node == null)
                node = document;
            var classElements = [],
                els = node.getElementsByTagName("*"),
                elsLen = els.length,
                pattern = new RegExp("(^|\\s)" + searchClass + "(\\s|$)"),
                i, j;

            for (i = 0, j = 0; i < elsLen; i++) {
                if (pattern.test(els[i].className)) {
                    classElements[j] = els[i];
                    j++;
                }
            }
            return classElements;
        })(classname, node);
    }
}

function copyToClipboard(text) {
    var copyDiv = document.createElement('div');
    copyDiv.contentEditable = true;
    document.body.appendChild(copyDiv);
    copyDiv.innerHTML = text;
    copyDiv.unselectable = "off";
    copyDiv.focus();
    document.execCommand('SelectAll');
    document.execCommand("Copy", false, null);
    document.body.removeChild(copyDiv);

    return true;
}
// End helper functions

// Main
function main() {
    var title = getElementsByClassName(document, 'card-detail-title-assist')[0].innerText;
    var prefix = title.match(/s\d+_c\d+/i);
    var hasPrefix = prefix != undefined;

    if (hasPrefix) {
        var branch = 'BCH_' + prefix[0];
        console.log('Get Branch: "' + branch + '" copiado!');
        chrome.runtime.sendMessage({status: true});

        return copyToClipboard(branch);
    }

    return alert('Este cartão não tem um prefixo S000_C000 válido!');
}

main();