Js variables, scopes, and memory _ basic knowledge

This article mainly analyzes JS variables, scopes, and memory issues in detail, and attaches a lot of examples to help you understand these three concepts. It is a rare article, we hope to help you with the following basic types: undefined, NUll, Boolean, Number, and String. These types occupy a fixed size space in the memory, and their values are stored in the stack space, we access it by value.

(1) Value Type: numerical value, Boolean value, null, undefined.
(2) reference type: object, array, and function.

If the value is a reference value, you must allocate space for this value in the heap memory. Because the size of this value is not fixed (the object has many attributes and methods), they cannot be saved to the stack memory. However, the memory address size is fixed, so the memory address can be stored in the stack memory.