How to execute a code encoded in base64 in Javascript

Question

I have this code in an html page (JavaScript):

<script>
    var cox,d = 0;
    Console.Log(cox,d);
</script>

Now I encrypted [var cox,d = 0; Console.Log(cox,d);] manually with base64 encode and the result is this: IHZhciBjb3gsZCA9IDA7DQogQ29uc29sZS5Mb2coY294LGQpOw==

I want that this encoded string (the code) could be executed by another JavaScript function in the same page... example:

<script>
    var encoded = "IHZhciBjb3gsZCA9IDA7DQogQ29uc29sZS5Mb2coY294LGQpOw==";
    var decodedString = atob(encoded);
    /* Problem is here */
</script>

I want to execute the JavaScript code (encoded above) in /* Problem is here */ '.

How can I do?

Just being pedantic, encoding with BASE64 and encrypting is not the same thing at all. I think you want to use `eval` - but that is a slippery slope :) — Morten Jensen, Feb 05 '18 at 14:27
my pc changed it from console to Console automatically because I coded it on stack overflow not on an editor first.... — Programmer, Feb 05 '18 at 19:11

score 6 · Accepted Answer · answered Feb 05 '18 at 14:43

You can use the eval function (it is not recommended), but it solves your problem.

/* var cox,d = 0; console.log(cox,d); */
var encoded = "dmFyIGNveCxkID0gMDsgY29uc29sZS5sb2coY294LGQpOw==";
var decodedString = atob(encoded);


eval(decodedString);

Another way of doing it, is using the New Function constructor

/* var cox,d = 0; console.log(cox,d); */
var encoded = "dmFyIGNveCxkID0gMDsgY29uc29sZS5sb2coY294LGQpOw==";
var decodedString = atob(encoded);

var func = new Function(decodedString);
func();

*When encodeding your code, Console and Log must be lowercase and not ucfirst.

I am not a security expert, and I truely advice you to check the risks of evaluating and executing this kind of functions in your apps.

Here is an interesting answer about the difference between eval and new Function

Thank you very much... The second works properly for me and is what I was looking for... — Programmer, Feb 05 '18 at 19:08

How to execute a code encoded in base64 in Javascript

1 Answers1