Slide 1

Declaring a variable

To use a variable, you've first got to create it — more accurately, we call this declaring the variable. To do this, we type the keyword var or let followed by the name you want to call your variable:

 let myName;
 let myAge;

Here we're creating two variables called myName and myAge. Try typing these lines into your web browser's console. After that, try creating a variable (or two) with your own name choices.

Note: In JavaScript, all code instructions should end with a semi-colon (;) — your code may work correctly for single lines, but probably won't when you are writing multiple lines of code together. Try to get into the habit of including it.

Slide 2

You can test whether these values now exist in the execution environment by typing just the variable's name, e.g.

 myName;
 myAge;

They currently have no value; they are empty containers. When you enter the variable names, you should get a value of undefined returned. If they don't exist, you'll get an error message — try typing in

 scoobyDoo;

Note: Don't confuse a variable that exists but has no defined value with a variable that doesn't exist at all — they are very different things. In the box analogy you saw above, not existing would mean there's no box (variable) for a value to go in. No value defined would mean that there IS a box, but it has no value inside it.