How to De-obfuscate Javascript code. Easy way

Step 1: Access link http://www.jsnice.org/ and paste code javascript.
- Decode.
Step 2: Replace value in array was be decoded.
var _html  = all code;
function GetIndexByValue(arr, ){
for(var i=0, k=arr.length; i < k; i++) {
_html = _html.replace("name of array[" + i + "]", "\"" + arr[i] + "\"");
}
}


for(var i = 0 ; i < 20; i++){
GetIndexByValue();
}