Coding Challenge Practice - Question 81

The task is to implement a function that replaces undefined with null.

The boilerplate code

function undefinedToNull(arg) {
  // your code here
}

If it is a single value

if(arg === undefined) return null;

If the value is an array, create a new array with the same length

 if(Array.isArray(arg)) {
    const result = new Array(arg.length);
  }

Go through each element one by one, then run it recursively for each element

    for(let i = 0; i < arg.length; i++) {
      result[i] = undefinedToNull(arg[i]);
    }

If the value is an object, create a new empty object

if(arg !== null && typeof arg === 'object') {
    const result = {};
  }

Go through every key in the object, apply the function to each value and assign the result back to the same key

    for(const key in arg) {
      result[key] = undefinedToNull(arg[key]);
    }

The final code

function undefinedToNull(arg) {
  // your code here
  if(arg === undefined) return null;

  if(Array.isArray(arg)) {
    const result = new Array(arg.length);
    for(let i = 0; i < arg.length; i++) {
      result[i] = undefinedToNull(arg[i]);
    }
    return result;
  }

  if(arg !== null && typeof arg === 'object') {
    const result = {};
    for(const key in arg) {
      result[key] = undefinedToNull(arg[key]);
    }
    return result;
  }
  return arg;
}

That's all folks!