获取文件后缀名
/**
 * 获取文件后缀名
 * @param {String} filename
 */
 export function getExt(filename) {
    if (typeof filename == 'string') {
        return filename
            .split('.')
            .pop()
            .toLowerCase()
    } else {
        throw new Error('filename must be a string type')
    }
}
复制内容到剪贴板
export function copyToBoard(value) {
    const element = document.createElement('textarea')
    document.body.appendChild(element)
    element.value = value
    element.select()
    if (document.execCommand('copy')) {
        document.execCommand('copy')
        document.body.removeChild(element)
        return true
    }
    document.body.removeChild(element)
    return false
}