📘 JavaScript apply()

✅ 1. What Is apply()?

The apply() method allows you to invoke a function, while explicitly specifying:

• The this context
• The arguments (as an array or array-like object)

jsCopyEditfunction sayHello() {
  console.log("Hello, " + this.name);
}

const user = { name: "Alice" };

sayHello.apply(user); // Hello, Alice

📌 2. Syntax

jsCopyEditfunc.apply(thisArg, [arg1, arg2, ...])

• func: the function to be called
• thisArg: the value to use as this when the function runs
• []: an array of arguments

📌 3. Example: Passing Arguments with apply()

jsCopyEditfunction introduce(language1, language2) {
  console.log(`${this.name} speaks ${language1} and ${language2}`);
}

const person = { name: "Bob" };

introduce.apply(person, ["English", "French"]);
// Output: Bob speaks English and French

📌 4. Difference Between call() and apply()

Example:

jsCopyEditfunc.call(thisArg, arg1, arg2);
func.apply(thisArg, [arg1, arg2]);

📌 5. Use Case: Math.max with Arrays

You can’t pass an array directly to Math.max, but you can use apply():

jsCopyEditconst nums = [10, 30, 5, 8];
const max = Math.max.apply(null, nums);

console.log(max); // 30

✅ Works because apply() spreads the array into individual arguments.

📌 6. Use Case: Borrowing Methods

jsCopyEditconst arrayLike = {
  0: "a",
  1: "b",
  length: 2
};

// Borrow Array method
const realArray = Array.prototype.slice.apply(arrayLike);

console.log(realArray); // ["a", "b"]

📌 7. ES6 Replacement: Spread Operator

In modern JavaScript, the spread syntax often replaces apply():

jsCopyEditMath.max(...[10, 20, 30]); // 30

But apply() is still useful in older environments and for method borrowing.

🧪 Practice Tasks

1. Create a function greetUser(greeting) and use apply() to pass { name: "Sam" } and ["Good morning"].
2. Use Math.min.apply() to find the smallest number in [3, 8, -5, 12].

🧠 Summary

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