immut.es5.js

"use strict";

var immut = (function () {

  var descriptor = {
    value: null
  };

  return function immut() {
    if (arguments.length % 2 !== 0)
      throw new Error('Requires an even number of arguments!');

    var obj = {};

    for (var i = 0, len = arguments.length; i < len; i += 2) {
      descriptor.value = arguments[i + 1];
      Object.defineProperty(obj, arguments[i], descriptor);
    }

    descriptor.value = null;
    Object.preventExtensions(obj);
    return obj;
  };

}());

immut.js

"use strict";

let immut = (function () {

  let descriptor = {
    value: null
  };

  return (...args) => {
    if (args.length % 2 !== 0)
      throw new Error('Requires an even number of arguments!');

    let obj = {};

    for (let i = 0, len = args.length; i < len; i += 2) {
      descriptor.value = args[i + 1];
      Object.defineProperty(obj, args[i], descriptor);
    }

    descriptor.value = null;
    Object.preventExtensions(obj);
    return obj;
  };

}());

// Usage:
//
// let a = immut("foo", 1,
//               "bar", 2);
//
// a.baz = 3; // Error: a is not extensible
// a.foo = 4; // Error: "foo" is read-only