Why Are JavaScript Strings Immutable, and When Would You Need a String Builder?

Are JavaScript Strings Immutable? Exploring the Need for a "String Builder"

JavaScript strings, unlike their counterparts in many other programming languages, possess an immutable nature. This means that operations performed on strings do not modify the original string but instead return a new string.

String Immutability Demonstration

Consider the following example:

var myString = "Hello";
myString[2] = 'c';
console.log(myString); // Output: "Hello"

As seen, the attempt to modify the character at index 2 of myString has no effect on its original value.

Implications of Immutability

This immutability has several implications:

• String manipulation methods like trim() and slice() always produce new strings.
• If you have multiple references to the same string, modifying one will not affect the others.

Debunking the Concatenation Speed Myth

Traditionally, it was believed that using Array.join() for concatenating strings was faster than direct string concatenation. However, benchmarks have proven this notion to be incorrect.

Custom "String Builder"

Given the immutability of strings, one might consider implementing a custom "string builder" to optimize concatenation efficiency. However, as demonstrated by our benchmarks, string concatenation performs surprisingly well in JavaScript.

In conclusion, JavaScript strings are immutable, and while a custom "string builder" may seem tempting, it is typically not necessary for performance optimization in most cases.

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