Immutability Helper - Video Solutions

Creating clones of immutable objects with minor alterations can be a tedious process. Write a class ImmutableHelper that serves as a tool to help with this requirement. The constructor accepts an immutable object obj which will be a JSON object or array.

The class has a single method produce which accepts a function mutator. The function returns a new object which is similar to the original except it has those mutations applied.

mutator accepts a proxied version of obj. A user of this function can (appear to) mutate this object, but the original object obj should not actually be effected.

For example, a user could write code like this:

const originalObj = {"x": 5};
const helper = new ImmutableHelper(originalObj);
const newObj = helper.produce((proxy) => {
  proxy.x = proxy.x + 1;
});
console.log(originalObj); // {"x": 5}
console.log(newObj); // {"x": 6}

Properties of the mutator function:

• It will always return undefined.
• It will never access keys that don't exist.
• It will never delete keys (delete obj.key)
• It will never call methods on a proxied object (push, shift, etc).
• It will never set keys to objects (proxy.x = {})

Note on how the solution will be tested: the solution validator will only analyze differences between what was returned and the original obj. Doing a full comparison would be too computationally expensive. Also, any mutations to the original object will result in a wrong answer.

 

Example 1:

Input: 
obj = {"val": 10}, 
mutators = [
  proxy => { proxy.val += 1; },
  proxy => { proxy.val -= 1; }
]
Output: 
[
  {"val": 11},
  {"val": 9}
]
Explanation:
const helper = new ImmutableHelper({val: 10});
helper.produce(proxy => { proxy.val += 1; }); // { "val": 11 }
helper.produce(proxy => { proxy.val -= 1; }); // { "val": 9 }

Example 2:

Input: 
obj = {"arr": [1, 2, 3]} 
mutators = [
 proxy => { 
   proxy.arr[0] = 5; 
   proxy.newVal = proxy.arr[0] + proxy.arr[1];
 }
]
Output: 
[
  {"arr": [5, 2, 3], "newVal": 7 } 
]
Explanation: Two edits were made to the original array. The first element in the array was to set 5. Then a new key was added with a value of 7.

Example 3:

Input: 
obj = {"obj": {"val": {"x": 10, "y": 20}}}
mutators = [
  proxy => { 
    let data = proxy.obj.val; 
    let temp = data.x; 
    data.x = data.y; 
    data.y = temp; 
  }
]
Output: 
[
  {"obj": {"val": {"x": 20, "y": 10}}}
]
Explanation: The values of "x" and "y" were swapped.

 

Constraints:

• 2 <= JSON.stringify(obj).length <= 4 * 105
• mutators is an array of functions
• total calls to produce() < 105