Autoboxing Primitive Types in JavaScript

Tyler Clark
InstructorTyler Clark

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Published 2 years ago
Updated 10 months ago

Primitive values by rule are not objects. However when we treat a primitive type like an object, such as getting the .length of a string, JavaScript will wrap that primitive type into an object. This new object is then linked to the corresponding built-in .prototype, so that we can utilize prototype methods on primitive types.

Instructor: [00:00] If you're working in JavaScript, you're bound to hear someone tell you at one point in your career that everything in JavaScript is an object. However, there are primitive types that are used every day that are not objects. There is a reason though why this saying has come about and why it sticks around.

[00:16] Primitive types like our string here are not objects. They cannot be dotted into liken object. They don't have properties or methods on them. With this in mind, we should see some type of error when we get the length of a string, right?

[00:29] This is, again, because by rule, primitive values such as our string, number, Boolean, and etc., don't have properties on them, they don't have methods. However, as we see here, this is not the case. We get a returned value.

[00:44] What we can't see behind the scenes is JavaScript is doing something called autoboxing. Autoboxing happens automatically whenever we treat a primitive type like an object. In other words, whenever we try to .length on a string for example or toString a number, or get the value of a Boolean. Which means we are dotting into these primitives.

[01:06] JavaScript will wrap those primitives into an object. With this new object, it will connect it to the built-in object prototype that corresponds with that primitive type. Which thus, gives us access to the built-in dot prototype methods from the browser.

[01:24] Going back to my original statement of everything in JavaScript being an object, with primitive types, this is not true. But because of autoboxing where, when we treat primitive types like an object and JavaScript wrapping those primitives into objects, you can see why this misconception has started and is here today.

Michael
Michael
~ 2 years ago

But there are a lot of methods on strings, ie padEnd.

Rafael Melo
Rafael Melo
~ a year ago

"Primitive values by rule are not objects. However when we treat a primitive type like an object, such as getting the .length of a string, JavaScript will wrap that primitive type into an object. "

Joey Ng'ethe
Joey Ng'ethe
~ a year ago

@tyler, what tool/extension do you use to show the console.log values inside the editor?