A JS implementation of Ruby's constantize

constantize.js

// A basic example of how Ruby's constantize _could_ work in JS
// See https://apidock.com/rails/String/constantize
function constantize (str) {
  if (typeof str !== 'string') {
    throw new TypeError('must pass in type of string');
  }

  if (str.match(/\W|\d/)) {
    throw new SyntaxError('must pass in a valid Javascript name');
  }
  else {
    var constant
    eval("constant = " + str);
    return constant;
  }
};

Why not just return eval(str);

Whenever possible, a collection of objects with a object key lookup is much faster than eval:

https://jsperf.com/constantize-eval-vs-obj-key

Neat use of eval though!