基础

function funGetClass(className) {
    if(document.getElementsByClassName) {
        return document.getElementsByClassName(className);
    }
    var aClassDiv = [];
    var aAll = document.getElementsByTagName("*");
    for(var i= 0,l=aAll.length;i<l;i++) {
        if (aAll[i].className.indexOf(className)+1) {
            aClassDiv.push(aAll[i]);
        }
    }
    return aClassDiv;
}
function fun$(string) {
    var perName = string.charAt(0);
    var suxName = string.substr(1);
    switch (perName) {
        case "#": document.getElementById(suxName);break;
        case ".": funGetClass(suxName);break;
        default: document.getElementsByTagName(string);break;
    }
}