js怎么实现复制文本

if (navigator.clipboard) {
    navigator.clipboard.writeText('test text');
    showTips('复制成功!', 30, 2);
} else {
    const eventCopyer = event => {
        event.preventDefault();
        event.clipboardData.setData("text/plain", 'test text');
    }
    document.addEventListener("copy", eventCopyer);
    document.execCommand("copy");
    document.removeEventListener("copy", eventCopyer);
}