How to Use call() in JavaScript: Syntax and Examples

In JavaScript, call() is a method used to invoke a function with a specified this context and individual arguments. It allows you to control what this refers to inside the function when calling it.

Syntax

The call() method syntax is:

• functionName.call(thisArg, arg1, arg2, ...)

Here, functionName is the function you want to call.

thisArg is the object to use as this inside the function.

arg1, arg2, ... are the arguments passed to the function.

javascript

functionName.call(thisArg, arg1, arg2, ...);

Example

This example shows how to use call() to set this inside a function and pass arguments:

javascript

const person = {
  fullName: function(city, country) {
    return this.firstName + " " + this.lastName + ", " + city + ", " + country;
  }
};

const person1 = {
  firstName: "John",
  lastName: "Doe"
};

const result = person.fullName.call(person1, "New York", "USA");
console.log(result);

Output

John Doe, New York, USA

Common Pitfalls

Common mistakes when using call() include:

• Not passing the correct this object, which can cause errors or unexpected results.
• Passing arguments as an array instead of individual values (use apply() for arrays).
• Forgetting that call() immediately invokes the function.

javascript

const obj = { name: "Alice" };

function greet(greeting) {
  console.log(greeting + ", " + this.name);
}

// Wrong: passing arguments as array (does not work with call)
greet.call(obj, ["Hello"]); // Outputs: Hello, Alice (but argument is an array, not string)

// Right: pass arguments individually
greet.call(obj, "Hello"); // Outputs: Hello, Alice

Output

Hello, Alice
Hello, Alice

Quick Reference

Method	Purpose	Arguments
call()	Calls function with specified this and individual args	thisArg, arg1, arg2, ...
apply()	Calls function with specified this and args as array	thisArg, [argsArray]
bind()	Returns new function with bound this and optional args	thisArg, arg1, arg2, ...

Key Takeaways

call() invokes a function with a specified this value and individual arguments.

Always pass the correct object as thisArg to control the function context.

Use individual arguments with call(), not arrays (use apply() for arrays).

call() immediately runs the function; it does not create a new function.

It helps reuse functions with different objects easily.