function $(className) {
    var newClassName = className.split(" ");
    if (newClassName.length > 1) {
        var father = newClassName[newClassName.length - 2];
        var childrenList = document.querySelector(father).children;

        var arr = Array.from(childrenList).filter(function (el){
            if (
                el.className.indexOf( (newClassName[newClassName.length-1]).replace(".", "") ) > -1
                ||
                el.tagName.toLowerCase() == newClassName[newClassName.length-1]
            ) {
                return el;
            }
        });

        if (arr.length > 1) {
            return document.querySelectorAll(className)
        } else if (arr.length == 1){
            return document.querySelector(className)
        } else {
            throw new Error(`${className} 不存在，请检查`)
        }

    } else {
        return document.querySelector(newClassName);

    }
}