Understanding String Immutability in JavaScript

In JavaScript, strings are immutable, meaning they cannot be changed once they are created. This fundamental concept ensures that any modification to a string results in the creation of a new string, leaving the original unchanged.

What Does Immutability Mean?

In JavaScript, all strings are immutable.
Immutable means that an existing string cannot be altered.
No direct modifications can be made to strings.
Whenever we try to modify a string, a new string is created while the old one remains unchanged.

When we apply a method to a string or perform an operation on it, a new string is created instead of modifying the existing one.

Example of String Immutability

Consider the following example where we use the .trim() method to remove extra spaces from a string:

Code Example

let msg = "  inder  ";
console.log(msg.trim());

Console Output

"inder"

Even though .trim() appears to modify the msg string, it actually creates a new string with spaces removed. The original msg variable still holds the same value.

Understanding Through Another Example

let text = "Hello";
text.toUpperCase();
console.log(text);

Output:

"Hello"

Even though we applied .toUpperCase(), the text variable remains unchanged because strings are immutable. To actually store the modified value, we need to assign it to a new variable:

let newText = text.toUpperCase();
console.log(newText);

New Output:

"HELLO"

Key Takeaways

Strings in JavaScript cannot be modified directly.
Any modification results in a new string being created.
To work with modified strings, we must store them in a new variable.
This behavior is important for memory efficiency and helps prevent accidental changes to existing data.

( String are immutable ) What is String Immutability in JavaScript?

Table of contents