javascript(js)使用eval方法加密过的函数解密方法

<script>
a=62;
function encode() {
var code = document.getElementById('code').value;
code = code.replace(/[ ]+/g, '');
code = code.replace(/'/g, "/'");
var tmp = code.match(/(w+)/g);
tmp.sort();
var dict = [];
var i, t = '';
for(var i=0; i<tmp.length; i++) {
if(tmp[i] != t) dict.push(t = tmp[i]);
}
var len = dict.length;
var ch;
for(i=0; i<len; i++) {
ch = num(i);
code = code.replace(new RegExp('/b'+dict[i]+'/b','g'), ch);
if(ch == dict[i]) dict[i] = '';
}
document.getElementById('code').value = "eval(function(p,a,c,k,e,d){e=function(c){return(c<a?'':e(parseInt(c/a)))+((c=c%a)>35?String.fromCharCode(c+29):c.toString(36))};if(!''.replace(/^/,String)){while(c--)d[e(c)]=k[c]||e(c);k=[function(e){return d[e]}];e=function(){return'//w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('//b'+e(c)+'//b','g'),k[c]);return p}("
+ "'"+code+"',"+a+","+len+",'"+ dict.join('|')+"'.split('|'),0,{}))";
}

function num(c) {
return(c<a?'':num(parseInt(c/a)))+((c=c%a)>35?String.fromCharCode(c+29):c.toString(36));
}

function run() {
eval(document.getElementById('code').value);
}

function decode() {
var code = document.getElementById('code').value;
code2 = code.replace(/^eval/, '');
//alert(code);
document.getElementById('code').value = eval(code2);
}

<textarea id=code cols=80 rows=20>