how declare variable and not assign value in js code example

Example 1: how to declare variables javascript

//variables are a way to easily store data in javascript
//variables are declared by the var keyword, example...
var x = 10;
//or
var dog_name = "daisy";
//which can also be written as 
var dog_name = 'daisy';
//same thing with single quotes and double quotes

Example 2: varaible javascript

let <var-name> = value;