Very important concept to understand, I’ll need to start with some context.
Context of Hoisting
We need to understand the life cycle of code and there are two main phases code goes through. The Creation Phase and the Execution Phase.
When does hoisting happen?
During the Creation Phase, the program will set all the global variables and if there are var variables declared they will be initialized with the value of ‘undefined’, upon the programs Execution Phase this will assign the value officially to the variable if the var is above the invoked function.
MDN definition:
The var statement declares a function-scoped or globally-scoped variable, optionally initializing it to a value.
My understanding of hoisting is:
The process of a variable(var, let, const) declaration a default value of undefined during the creation phase. Functions on the other hand upon starting up of the program are stored in memory source
The above tutorial also goes through other important concepts of JavaScript functions and their behavior when invoked.