Checking if a Map or Set is Empty in JavaScript

When working with JavaScript’s Map and Set objects, it’s common to need to check if they are empty. Lets explore different ways to achieve this in JS.

Using the Size Property

Both Map and Set objects have a size property, which represents the number of elements in the collection. Checking if this property is equal to zero is a straightforward way to determine if the Map or Set is empty.

const emptyMap = new Map();
const nonEmptyMap = new Map([[1, 'one'], [2, 'two']]);

console.log(emptyMap.size === 0);       // Output: true
console.log(nonEmptyMap.size === 0);    // Output: false

const emptySet = new Set();
const nonEmptySet = new Set([1, 2, 3]);

console.log(emptySet.size === 0);       // Output: true
console.log(nonEmptySet.size === 0);    // Output: false

This concise approach leverages the power of Array.from() to create a mapped array.

Checking for Existence of Elements

For Sets, you can directly check the existence of elements using the has method. For Maps, this involves checking if the size property is zero.

const emptyMap = new Map();
const nonEmptyMap = new Map([[1, 'one'], [2, 'two']]);

console.log(emptyMap.size === 0);       // Output: true
console.log(nonEmptyMap.size === 0);    // Output: false

const emptySet = new Set();
const nonEmptySet = new Set([1, 2, 3]);

console.log(emptySet.size === 0);       // Output: true
console.log(nonEmptySet.size === 0);    // Output: false

Using the forEach Method

Another approach is to use the forEach method to iterate through the elements. If the callback function is never called, it means the collection is empty. Weird, but yeah, can do.

function isEmpty(collection) {
  let empty = true;
  collection.forEach(() => (empty = false));
  return empty;
}

const emptyMap = new Map();
const nonEmptyMap = new Map([[1, 'one'], [2, 'two']]);

console.log(isEmpty(emptyMap));       // Output: true
console.log(isEmpty(nonEmptyMap));    // Output: false

const emptySet = new Set();
const nonEmptySet = new Set([1, 2, 3]);

console.log(isEmpty(emptySet));       // Output: true
console.log(isEmpty(nonEmptySet));    // Output: false

🧪Practice Coding Problem: Task and Feedback Manager

In the spirit of Test Driven Development ( 😁), lets test our understanding by solving a problem.

You are building a small application to manage tasks and user feedback. Using JavaScript’s Map and Set, tasks are stored in a Map, and feedback is tracked with a Set.

Write a function hasFeedback that takes the tasks (Map) and feedback (Set) as parameters, along with a task ID. The function should return true if the specified task has received feedback and false otherwise.

JavaScript

function hasFeedback(tasks, feedback, taskId) {
  // > > > 👉 Write code here 👈 < < <
}

const tasks = new Map([
  [1, { description: 'Complete assignment' }],
  [2, { description: 'Prepare presentation' }],
]);

const feedback = new Set([1]);

console.log(hasFeedback(tasks, feedback, 1)); // Output: true
console.log(hasFeedback(tasks, feedback, 2)); // Output: false

Constraints:

• Task IDs are positive integers.
• The tasks Map will have at most 100 entries.
• The feedback Set will have at most 100 entries.

function hasFeedback(tasks, feedback, taskId) {
  // Check if the task ID exists in the tasks Map
  if (tasks.has(taskId)) {
    // Check if the task ID is in the feedback Set
    return feedback.has(taskId);
  } else {
    // Task with the specified ID doesn't exist
    return false;
  }
}

// Example Usage:
const tasks = new Map([
  [1, { description: 'Complete assignment' }],
  [2, { description: 'Prepare presentation' }],
]);

const feedback = new Set([1]);

console.log(hasFeedback(tasks, feedback, 1)); // Output: true
console.log(hasFeedback(tasks, feedback, 2)); // Output: false

OK, so if you are checking if a collection is empty, then just use the size property or loop through elements. The only thing you can’t check is if the coffee pot in the office is empty—no JS magic for that! ☕ But I digressed, you keep coding🚀!