Are JavaScript strings immutable? Do I need a “string builder” in JavaScript?

Question

Does javascript use immutable or mutable strings? Do I need a \"string builder\"?

Answer 1

Just to clarify for simple minds like mine (from MDN):

Immutables are the objects whose state cannot be changed once the object is created.

String and Numbers are Immutable.

Immutable means that:

You can make a variable name point to a new value, but the previous value is still held in memory. Hence the need for garbage collection.

var immutableString = "Hello";

// In the above code, a new object with string value is created.

immutableString = immutableString + "World";

// We are now appending "World" to the existing value.

This looks like we're mutating the string 'immutableString', but we're not. Instead:

On appending the "immutableString" with a string value, following events occur:

1. Existing value of "immutableString" is retrieved
2. "World" is appended to the existing value of "immutableString"
3. The resultant value is then allocated to a new block of memory
4. "immutableString" object now points to the newly created memory space
5. Previously created memory space is now available for garbage collection.