[Medium] LeetCode JS 30 - 2705. Compact Object

Question Prompt

Let's say you're tasked with cleaning up an array by removing any falsey values. Can you walk through how you'd implement a function called compact(array) that achieves this? Keep in mind that falsey values in this context include false, null, 0, empty strings, undefined, and NaN.

compact([0, 1, false, 2, "", 3, "hello"]); // [1, 2, 3, 'hello']
compact([null, undefined, NaN, " "]); // [' ']
compact([{ name: "Alice" }, null, { age: 30 }, undefined]); // [{ name: 'Alice' }, { age: 30 }]

Solutions

• Starts by creating an empty array called result. This array will eventually hold the compacted elements.
• The for...of loop steps through each value in the original array.
• The if (value) conditional statement is crucial. It leverages JavaScript's concept of truthy and falsy values.
  • Truthy values, like non-zero numbers, non-empty strings, and objects, will pass this check.
  • Falsy values, like false, null, 0, empty strings, undefined, and NaN, will fail and be excluded from the result.
• If a value passes the truthiness check, it's added to the result array using the result.push(value) method.
• Once the loop completes, the function returns the result array, which now contains only the truthy values from the original input array.

function compact(array) {
  const result = [];
  for (const value of array) {
    if (value) {
      result.push(value);
    }
  }
  return result;
}

Or we can take a more concise approach to compacting the array, utilizing the built-in filter method in JavaScript.

• The array.filter(Boolean) call applies the filter method directly to the input array.
• The Boolean function is passed as a predicate to filter. This function acts as a decision-maker for each element.
• For each element in the array, Boolean is implicitly called on it. Truthy values return true, while falsy values return false.
• The filter method constructs a new array, including only those elements for which the predicate (in this case, Boolean) returned true.
• The function directly returns this new, filtered array, containing only the truthy elements from the original input.

function compact(array) {
  return array.filter(Boolean);
}