JavaScript Interview Guide: Difference Between apply() and call() Methods

Introduction

In JavaScript, both apply() and call() are methods used to invoke functions while explicitly setting the this context. While they serve similar purposes, their parameter handling differs. Understanding these differences is crucial for interviews and real-world coding scenarios.

Key Differences

Example: call()

function greet(message) {
  console.log(`${message}, ${this.name}!`);
}

const user = { name: 'Alice' };
greet.call(user, 'Hello'); // Output: "Hello, Alice!"

Example: apply()

function sum(a, b, c) {
  return a + b + c;
}

const numbers = [1, 2, 3];
console.log(sum.apply(null, numbers)); // Output: 6

When to Use Each?

• Use call() when arguments are known and fixed.
• Use apply() when arguments are dynamic (e.g., from an array).

Modern Alternative: bind() and Spread Operator

With ES6+, you can often replace apply() with the spread operator:

sum(...numbers); // Same result as apply()

Interview Tip

Interviewers often ask: “How would you use call() to borrow a method from another object?”
Example:

const car = { brand: 'Toyota' };
const showBrand = function() { console.log(this.brand); };
showBrand.call(car); // Output: "Toyota"

Conclusion

While call() and apply() achieve the same goal, their argument handling differs. Master both to write flexible code and ace JavaScript interviews.

Pro Tip: In modern JS, the spread operator reduces apply() usage, but understanding these methods remains vital for legacy code and interviews.