Javascript键盘事件的keyChar

Javascript的键盘事件keydown, keyup,  keypress的event对象中，keyCode !=  keyChar，网上有很多人提供了keyCode到keyChar的对照表。于是，根据对照表，产生了如下工具函数，只需要把event对象作为参数传进去，就能够得到keyChar了，如果keyCode没有对应的字符，那返回的就是'\0'。
window.keyChar = (function () {
    var ssss = "";
    var SSSS = "";
 
    // M和m只是标尺, ssss和SSSS变量长度是为了对齐标尺
    var M = "0         1         2         3         4         ";
    var m = "01234567890123456789012345678901234567890123456789";
 
    // 不带shift的码表
    ssss += "                                                01";
    ssss += "23456789       abcdefghijklmnopqrstuvwxyz     0123";
    ssss += "456789*+ -./                                      ";
    ssss += "                                     ;=.-,/`      ";
    ssss += "                   [ ]'                           ";
 
    // 带shift的码表
    SSSS += "                                                )!";
    SSSS += "@#$%^&*(       ABCDEFGHIJKLMNOPQRSTUVWXYZ     0123";
    SSSS += "456789*+ -./                                      ";
    SSSS += "                                     :+>_<?~      ";
    SSSS += "                   {|}                            ";
 
    // 将码表拆成字符数组
    var t = ssss.split("");
    var T = SSSS.split("");
 
    // 将所有空格替换成空字符
    var