JavaScript Easy technical 1 views 1 min read

What is the difference between const and Object.freeze?

Peer-reviewed by HireXTech Technical Panel • Updated for 2025/2026 hiring • Editorial standards
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Interviewer Expectations for this Question
01
Core Competency

Assesses fundamental understanding of JavaScript conventions, runtime behavior, and memory/performance considerations.

02
Evaluation Criteria

Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.

Comprehensive Model Answer Verified Solution

The main difference is that const applies to variables (bindings), while Object.freeze() applies to values (objects).

  1. const: Prevents the reassignment of a variable identifier. It ensures that the variable name always points to the same memory reference. However, if the variable holds an object or array, the *contents* of that object can still be modified.
  2. Object.freeze(): Prevents the modification of an object's properties. It makes the object immutable (you cannot add, remove, or change properties), but it does not affect the variable assignment itself (unless the variable is also declared with const).

Example:

```javascript
// Case 1: Using const (Reassignment prevented, Mutation allowed)
const person = { name: "John" };
person.name = "Doe"; // ✅ Allowed: The object is mutable
console.log(person.name); // "Doe"

// person = { name: "Jane" }; // ❌ Error: Assignment to constant variable

// Case 2: Using Object.freeze (Reassignment allowed, Mutation prevented)
let profile = { name: "John" };
Object.freeze(profile);

profile.name = "Doe"; // ❌ Ignored (or throws TypeError in strict mode)
console.log(profile.name); // "John"

profile = { name: "Jane" }; // ✅ Allowed: 'profile' is declared with 'let'
console.log(profile.name); // "Jane"

Candidate Response Strategy & Interview Tips

  1. Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
  2. Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
  3. Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
  4. Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.
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