In Javascript, you can declare a variable using “Var” or “let” BUT there is an inconvenient, don’t worry, I will give you context.
Some years ago(2015) Javascript changed. Var had a global scope before 2015, BUT with ecmascript6 it changed because We can use “Let” to declare a variable.
You shouldn’t use “Var” because it is considered a bad practice , It can get you into a value reassignment problem.
Example:

In this example I created a variable using “var” and printed on console three times to show you this…

You can see that the variable var was added to window’s global object.

BUT if you create a variable using LET, you won’t have that problem, and the variable LET could be a local or global variable.

I hope I have helped you by solving this question and You have saved time.
I look forward to your comments, have a nice day. =D