1. Implement function iterate(object, callback) to iterate given object passing each element to callback with the following contract callback(key, value, object). Example:

const obj = { a: 1, b: 2, c: 3 };
iterate(obj, (key, value) => {
  console.log({ key, value });
});

Output:

{ key: 'a', value: 1 }
{ key: 'b', value: 2 }
{ key: 'c', value: 3 }

2. Implement function store(value) to store value inside closure of returning function. After calling returning function it will return a value from closure, like in the following example:

const read = store(5);
const value = read();
console.log(value); // Output: 5

3. Implement function contract(fn, ...types) to wrap fn (first argument) and check argument types (all arguments except first and last) and result type (last argument). Generates TypeError exception if wrong types detected. As in following example:

const add = (a, b) => a + b;
const addNumbers = contract(add, Number, Number, Number);
const res = addNumbers(2, 3);
console.dir(res); // Output: 5

and

const concat = (s1, s2) => s1 + s2;
const concatStrings = contract(concat, String, String, String);
const res = concatStrings('Hello ', 'world!');
console.dir(res); // Output: Hello world!