invert.js

// Let's define how invert should work

// Given an object
// When invert is passed this object
// Then it should swap the keys and values in the object

// E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}

// leaving original code in for easier referral:

// function invert(obj) {
//  const invertedObj = {};
//
//  for (const [key, value] of Object.entries(obj)) {
//    invertedObj.key = value;
//  }
//
//  return invertedObj;
//}


// a) What is the current return value when invert is called with { a : 1 }
// the current return value is {key : 1 }

// b) What is the current return value when invert is called with { a: 1, b: 2 }
// the current return value is {key : 2} because the key is overwritten and 
// only the last value is stored

// c) What is the target return value when invert is called with {a : 1, b: 2}
// the target return value is {"1": "a", "2": "b"}

// c) What does Object.entries return? Why is it needed in this program?
// Object.entries converts an object into an array of [key, value] pairs. it is needed because
// for...of needs an array to work with 

// d) Explain why the current return value is different from the target output
// invertedObj.key = value creates a literal string with the name "key" instead of the value key.
// also, the current code assigns "value" to the new property instead of "key" 

// e) Fix the implementation of invert (and write tests to prove it's fixed!)

function invert(obj) {
  const invertedObj = {};

  for (const [key, value] of Object.entries(obj)) {
    invertedObj[value] = key;
  }

  return invertedObj;
}

// Tests
console.log(invert({ a: 1 })); // Expected output: { "1": "a" }
console.log(invert({ a: 1, b: 2 })); // Expected output: { "1": "a", "2": "b" }