Running JavaScript from the windows command prompt

Question

I wrote the following JavaScipt code which converts a binary number into a decimal number:

(function bin_dec(num) {
  var x = num;
  var result = 0;
  for (var i = 0; i < x.length; i++) {
    result += eval(x[x.length - i] * 2^i);
  }
  return result;
})()

I want to be able to run this code from the command-line. The filename is converter.js and I am running the command prompt window in the same directory as the file. I am trying to run this code using 01001100 as the function argument. Here are my attempts:

$ converter.js 01001100

and

$ converter.js -01001100

and

$ converter.js bin_dec(01001100)

But unfortunately, neither of these works. Can somebody please point out my mistake? Thanks in advance.

Answer 1

1) Install Node.js if you haven't done so yet.

2) Change your converter.js file like this:

function bin_dec(num) {
  return parseInt(num, 2);
}

console.log(bin_dec(process.argv[2]));

3) Open a new command prompt in the folder where your script is and run

$ node converter.js 01001100

Answer 2

In nodejs, assuming that you already have it installed since you are trying to run javascript from cmd, you will have to refer to the process.argv array in order to get the arguments passed in the command line.

So your code will need to look like this:

(function bin_dec(num) {
  var x = num;
  var result = 0;
  for (var i = 0; i < x.length; i++) {
    result += eval(x[x.length - i] * 2^i);
  }
  return result;
})(process.argv[2])

Notice process.argv[2] that is passed to the function. That will make the first argument available as the num variable inside your function.

You may also add a console.log somewhere if you want to have messages displayed on the screen, since the return statement will not print messages.

Answer 3

Assuming you are running on Windows, You can call it like this:

(function bin_dec() {
  var x = WScript.arguments(0);
  var result = 0;
  for (var i = 0; i < x.length; i++) {
    result += eval(x[x.length - i] * 2^i);
  }
  return result;
})()

Where all parameters passed into the function are stored in WScript.arguments.

However, this will not output the return value to the command prompt, so you may want to test it out with this .js file:

(function ShowAlert() {
  var x = WScript.arguments(0);
  WScript.ECho(x);
})()

See these links for more details:

MSDN - Arguments Property

SS64 - WScript Arguments

SS64 - VBScript Command line arguments