why don't use variable in number

Answer 1

What do you mean? can you show an example of what you don't understand?

Answer 2

var 4=100 ? why in this method don't follow

Answer 3

a variable just simply never start with a number, that just has no sens 4=4 not 100. The use of a variable must be understable just by reading the name the dev gave to it. People create languages agreed a var must start with a caracter a to z or underscore. To make sure people keep a clear synthax and because the motor reading your code must know rules, not something absolutly freedom.

Answer 4

In Javascript, variables cannot start with a number. Its one of the rules when giving a variable a name.