pipe js file to eval?

I am trying to pipe my aes.js file to eval because the file is too large. My code:

function onInit() {
  var fs = require('fs');

  var f = fs.readFile("aes.js");
  eval(f.pipe());
}

I get error:

Uncaught Error: Field or method does not already exist, and can't
create it on String at line 5 col 9 eval(f.pipe());

     ^ in function "onInit" called from line 1 col 8 onInit();