MEAN Cheat Sheet 2026

The 30 highest-yield MEAN facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What is the purpose of environment variables in a Node.js MEAN application? → Store configuration and secrets outside the codebase, accessed via process.env
2. In MongoDB, what is a capped collection? → A fixed-size collection that overwrites oldest documents when full
3. What is the purpose of MongoDB transactions introduced in version 4.0? → Provide ACID guarantees across multiple documents and collections
4. What is the purpose of Angular's `@ViewChild` decorator? → Gets a reference to a child component, directive, or DOM element in the template
5. How do you define a URL parameter in an Express route? → app.get('/users/:id', handler)
6. In MongoDB, what does the $group aggregation stage do? → Groups documents by a specified expression and accumulates values
7. What does the MongoDB `upsert` option do in an update operation? → Inserts a new document if no matching document exists
8. In order to convert Angular Components into native Custom Elements, which of the following APIs is used? → createCustomElement()
9. Which MongoDB write concern value ensures acknowledgment from a majority of replica set members? → majority
10. What is MongoDB's WiredTiger storage engine's default compression algorithm for documents? → Snappy
11. Where does Node.js operate? → Server
12. Use of Node.js is ideal in _______ → All of the above
13. Which Angular module must be imported to enable routing in an Angular application? → RouterModule
14. In Node.js _________ is the APIs of NOde.JS → Asynchronous
15. What is the difference between `@Input()` and `@Output()` decorators in Angular? → @Input() receives data from parent; @Output() emits events to the parent with EventEmitter
16. Which MongoDB aggregation stage is used to filter documents before passing them to the next stage in the pipeline? → $match
17. Which of the following Angular functions calls the iterator function? → angular.forEach
18. Which MongoDB feature allows data to automatically expire after a set time? → TTL (Time-To-Live) indexes
19. Which operator is used to atomically increment a numeric field in a MongoDB document? → $inc
20. Which directive marks the location in an Angular template where the routed component should be rendered? →
21. Which Express.js method sends a JSON response with the correct Content-Type header? → res.json()
22. What is the purpose of the `helmet` middleware in an Express application? → Sets security-related HTTP response headers to protect against common attacks
23. Which Express.js method is used to define a route that handles all HTTP methods? → app.all()
24. What is rate limiting in Express and which package is commonly used? → Limiting requests per time window using express-rate-limit to prevent abuse
25. In Angular, which character is used to enclose for property binding? → [
26. How many bytes does an object require? → 12
27. How do you create a template reference variable that holds the NgForm directive instance for validity checks? → #myForm="ngForm"
28. In Angular, which character is used to enclose for event binding? → (
29. In MongoDB, what does a 'covered query' mean? → A query satisfied entirely by an index without accessing documents
30. Which Angular feature allows you to define a template once and reuse it multiple times in a component? → ng-template with ngTemplateOutlet