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Grokking Node.js Design Patterns for Interviews

Problem: Auto-Default Missing Values

Easy
15 min
Return a default message when an accessed property doesn’t exist.

Problem statement

In your application, several components depend on configuration keys that may not exist yet. Currently, accessing a missing property simply returns undefined, which later causes runtime errors or confusing logs.

You want a safer approach: when a property is missing, it should return a default placeholder, such as "N/A", instead of undefined.

This will help modules safely read from incomplete configurations without crashing.

Goal

Wrap the given configuration object config in a Proxy that returns "N/A" whenever a non-existent property is accessed.

Constraints

  • You must use the get trap.

  • Do not modify the original object.

  • The Proxy should still return real values for existing keys.

  • Only missing keys should return the default placeholder.

Sample output

The examples below illustrate what the output should look like:

console.log(safeConfig.appName);   
/* Expected output:
'NodeMaster'
*/
console.log(safeConfig.debug);     
/* Expected output:
'N/A'
*/
console.log(safeConfig.version);   
/* Expected output:
'1.2.0'
*/
console.log(safeConfig.license);   
/* Expected output:
'N/A'
*/

Good luck trying the problem! If you’re unsure how to proceed, check the “Solution” tab above.

Similar Problems
Cache Expensive Function Calls via Proxy
Proxy a Remote Object over Network Simulation
Log Every Property Read on a Config Object
Prevent Accidental Mutation of Read-Only Settings
Lazy-Load a Heavy Service Only When First Used
Enforce Role-Based Access on Service Methods
Shape Legacy API Responses Without Touching the Source
Track API Usage Metrics Transparently
Home
Courses
Grokking Node.js Design Patterns for Interviews

Problem: Auto-Default Missing Values

Easy
15 min
Return a default message when an accessed property doesn’t exist.

Problem statement

In your application, several components depend on configuration keys that may not exist yet. Currently, accessing a missing property simply returns undefined, which later causes runtime errors or confusing logs.

You want a safer approach: when a property is missing, it should return a default placeholder, such as "N/A", instead of undefined.

This will help modules safely read from incomplete configurations without crashing.

Goal

Wrap the given configuration object config in a Proxy that returns "N/A" whenever a non-existent property is accessed.

Constraints

  • You must use the get trap.

  • Do not modify the original object.

  • The Proxy should still return real values for existing keys.

  • Only missing keys should return the default placeholder.

Sample output

The examples below illustrate what the output should look like:

console.log(safeConfig.appName);   
/* Expected output:
'NodeMaster'
*/
console.log(safeConfig.debug);     
/* Expected output:
'N/A'
*/
console.log(safeConfig.version);   
/* Expected output:
'1.2.0'
*/
console.log(safeConfig.license);   
/* Expected output:
'N/A'
*/

Good luck trying the problem! If you’re unsure how to proceed, check the “Solution” tab above.

Similar Problems
Cache Expensive Function Calls via Proxy
Proxy a Remote Object over Network Simulation
Log Every Property Read on a Config Object
Prevent Accidental Mutation of Read-Only Settings
Lazy-Load a Heavy Service Only When First Used
Enforce Role-Based Access on Service Methods
Shape Legacy API Responses Without Touching the Source
Track API Usage Metrics Transparently
Node.js
// Partial configuration
const config = {
  appName: 'NodeMaster',
  version: '1.2.0'
};
// Your code here
// Example usage
console.log(safeConfig.appName);   
/* Expected output:
'NodeMaster'
*/
console.log(safeConfig.debug);     
/* Expected output:
'N/A'
*/
console.log(safeConfig.version);   
/* Expected output:
'1.2.0'
*/
console.log(safeConfig.license);   
/* Expected output:
'N/A'
*/