When it comes to JavaScript, a String is considered a primitive value. However, it can also be treated as a String object. In programming terms, a primitive value refers to a value assigned directly to a variable.
This raises the question:
var d = "foo";
Does the variable d in this case contain the string "foo" directly or does it reference a string object similar to how other languages handle it?
Thank you for your help.
From my understanding, the variable d will store the string "foo" as a literal value and not as a reference to an object. However, JavaScript's engine will treat this literal as an instance of the String object when needed, allowing you to use methods from String.prototype on string literals like so:
"some string".toUpperCase(); //Method of String.prototype
Further clarification on this concept can be found in this excerpt from MDN:
String literals (enclosed in double or single quotes) and strings returned from non-constructor String calls are considered primitive strings. JavaScript automatically handles conversion between primitives and String objects, enabling the usage of String object methods on primitive strings by wrapping them when necessary for method invocation or property lookup.
While the technical details are covered in the specification, it may be challenging to grasp easily. I recently brought up a relevant topic in a discussion about why such operations are feasible on string literals, which offers a very detailed explanation worth exploring.
When you create a variable like
let x = "bar";
the value of x will be directly assigned as bar. However, if you create a variable using
let obj = new String("bar");
then obj will be treated as an Object.
For instance:
let y1 = "3";
let y2 = "3";
y1 == y2 -> true
let Obj1 = new String("4")
let Obj2 = new String("4");
Obj1 == Obj2 -> false
In my view, each variable in Javascript serves as an Object, with even a function being categorized as an Object.
After exploring the topic further, I came across a pair of informative articles that discuss this issue in depth. You can find them here and here. It appears that primitive types in JavaScript are passed by value, meaning they are isolated within functions when passed as arguments, preserving the original variable's value. On the other hand, reference types are passed by reference, allowing modifications to affect the original variable.
The primitive types in JavaScript include text (string), numeric (float/int), boolean, NULL, and the sometimes troublesome "undefined" type. Custom objects, functions, and standard arrays are examples of reference types. While I haven't delved into the specifics of the Date type, I suspect it falls under the category of primitive types.
Just stumbled upon this article on JavaScript strings, and it appears that:
The basic types in JavaScript include booleans, numbers, and strings.
In my opinion, Javascript does not have true primitives like Java does - every data type is essentially an object in some form.
Therefore, when you refer to a variable in Javascript, it is referencing an object - even if you modify the String object, d would reflect those changes.
If you're talking about built-in types in Javascript, there are some such as boolean, numbers, strings, and dates that are intrinsic to the language.
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