You can see what data types are primitives here on MDN: https://developer.mozilla.org/en-US/docs/Glossary/Primitive Technically, the differences can be subtle, but the big difference is that primitives are immutable, meaning you can't add to or modify properties within them like you can with objects. While you can have objects that are also immutable, primitives are always immutable. If you ever need to change a primitive value, it always has to be reassigned. It can't be modified. Primitives also generally represent a low-level value, not something complex. Things like numbers, strings and booleans make up primitives while more complex types like Dates and Arrays are defined by objects. Most primitives also have object variations of themselves. For example you can have the primitive number 5 or the number object new Number(5). However, you should almost always avoid the object version of primitive types and stick to using their primitive values. More on reddit.com

Same docs answer this question imo: Most of the time, a primitive value is represented directly at the lowest level of the language implementation. All primitives are immutable; that is, they cannot be altered. It is important not to confuse a primitive itself with a variable assigned a primitive value. The variable may be reassigned to a new value, but the existing value can not be changed in the ways that objects, arrays, and functions can be altered. The language does not offer utilities to mutate primitive values. Primitives have no methods but still behave as if they do. When properties are accessed on primitives, JavaScript auto-boxes the value into a wrapper object and accesses the property on that object instead. For example, "foo".includes("f") implicitly creates a String wrapper object and calls String.prototype.includes() on that object. This auto-boxing behavior is not observable in JavaScript code but is a good mental model of various behaviors — for example, why "mutating" primitives does not work (because str.foo = 1 is not assigning to the property foo of str itself, but to an ephemeral wrapper object). More on reddit.com

Now, cat is a variable of data type of object, and the object data represents the different key/value pairs (propreties), or the cat is an object? It's the same thing. Technically cat is a variable, and it holds an object (to be even more technical, it holds a reference to an object, but that's not the point). Saying "cat is an object" is a fairly common colloquial way to describe a variable and its type. For instance... let x = 1; I might say "x is a number". It's actually a variable that holds a number, but programmers are going to understand that's what I meant. More on reddit.com

Primitives are not objects. When you call a method on them they are temporarily wrapped in an object and unwrapped when the method is executed. More on reddit.com