JS code snippet - Unable to figure what the function does

Question

I am new to JS. I suspect it has something to do with the printout on console.

Can someone please help me understand what the function does in the following JS code snippet? Much appreciated!!

JS code snippet:

console.log("Registering Machines && Units...");

(function() {
  var P = ["\\", "|", "/", "-"];
  var x = 0;
  return setInterval(function() {
    process.stdout.write("\r" + P[x++]);
    x &= 3;
  }, 250);
})();

This would be a better question if you point out the specific parts of the code you're unclear on. — Jacob
– Jacob, Commented Oct 19, 2020 at 19:22

The code painter · Accepted Answer · 2020-10-19 19:39:25Z

1

this is basically a loading animation in console but not the browser but rather something like the command prompt .
you can think of process.stdout.write("\r" + P[x++]); as a console.log()
\r is a carriage return character; it tells your terminal emulator to move the cursor at the start of the line. The cursor is the position where the next characters will be rendered. So, printing a \r allows to override the current line of the terminal emulator.
x &= 3; is an AND bitwise operation which will ensure x is always set to 0 when it has surpassed 3 so that you have a kind of loop , because P.length is equal to 3 , its basically a short cut for doing this if(x>3)x=0
you can check this documentation https://www.w3schools.com/js/js_bitwise.asp

so all of this repeatedly prints the characters \\, |, /, - at the same position to give the illusion of a rotating | in the terminal.

edited Oct 19, 2020 at 19:39

answered Oct 19, 2020 at 19:25

The code painter

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