Your Template Engine Safely Accesses Deeply Nested Config Values Without Crashing on Missing Keys

Technical Interview Challenge: The "Safe-Path" Configuration Resolver

Context

In large-scale microfrontend architectures or complex CMS template engines, applications often consume deeply nested JSON configurations. A common runtime failure occurs when code attempts to access a property on an undefined or null intermediate key (the classic Cannot read property 'x' of undefined).

While modern JavaScript offers Optional Chaining (?.), many template engines and legacy utility libraries require a robust, string-based path resolver that can handle dynamic paths and provide fallback defaults to ensure the UI never crashes due to a malformed configuration.

Problem Statement

Implement a utility function get(obj, path, defaultValue) that retrieves a value from an object at a specified nested path. If the resolved value is undefined or if the path is unreachable, return the defaultValue.

Requirements:

1. Path Parsing: The path can be a string using dot notation (a.b.c) or bracket notation for arrays (a[0].b).

2. Null Safety: The function must handle null or undefined input objects gracefully without throwing an error.

3. Defaulting: If any segment of the path does not exist, the function should immediately bail and return the provided defaultValue.

4. Complex Keys: Assume the object may contain both nested objects and arrays.

Example Use Cases

Example 1: Standard Deep Access

JavaScript

Example 2: Array Indexing

JavaScript

Example 3: Missing Path with Default

JavaScript

Example 4: Handling Null Root

JavaScript