Question

There are several ways to take data (a string of code) and run it as part of the current program.

The most obvious way is the special operator eval , which will execute a string of code in the current scope. This is usually a bad idea because it breaks some of the sane properties that scopes normally have, such as being isolated from the outside world.

function evalAndReturnX(code) {
  eval(code);
  return x;
}

console.log(evalAndReturnX("var x = 2"));
// → 2

A better way of interpreting data as code is to use the Function constructor. This takes two arguments: a string containing a comma-separated list of argument names and a string containing the function’s body.

var plusOne = new Function("n", "return n + 1;");
console.log(plusOne(4));
// → 5

This is precisely what we need for our modules. We can wrap a module’s code in a function, with that function’s scope becoming our module scope.

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.