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Welcome back! Up to this point we've played around with some JavaScript types.

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Only 3 out of 7. Don't worry, we'll get to the rest of them.

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But there's one problem.

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How does the program remember things?

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For example, if we write "These pretzels are making me thirsty".

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And we'll do this.

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"+" We need the exclamation "!".

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OK.

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I enter that.

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OK. I get that. That's - that's good.

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But if I need to use this again.

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Well. Again I have to write "These pretzels

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are making me thirsty".

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And imagine if have to do that hundreds of times.

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That's kind of annoying right?

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That's - computers are supposed to help us but instead we just keep writing stuff and keep writing stuff.

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And that's not very efficient, is it?

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Well to catch and hold values

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JavaScript has something called variable's. And variables can be used

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with the word 'var'.

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So now if I go 'var george', so 'var george = "These pretzels are making me thirsty"'

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plus [+] "!".

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Notice the 'semicolon' here - I'll explain what that does in a bit.

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I press 'Enter'. I get 'undefined'.

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Let's not worry about that.

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That doesn't matter for now.

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And now if I go 'george' and you'll see that Google Chrome actually helps me and recognizes it.

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I press 'Enter'.

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"These pretzels are making me thirsty!". How awesome is that?

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So we're able to store this value.

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And obviously this is simple, but imagine, this was a long calculation that we had to make and we want

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to access it.

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Well, all we need to do now is have 'george'.

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It's a 'variable'.

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So now you see in the last video when I said that when we're comparing things we have to use '==='

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Well because when you do '3=3' it's saying: 'Assign the number 3 to 3'.

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But there's a rule with variables. With variables

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you can't start with numbers. So if I go 'var 3 = 3', I'll get an error.

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But if I go 'var three = 3', well, that's no problem.

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And variables have a few rules.

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The rules are: Well, it needs to start with a letter.

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It can end with a number, that's fine, but it needs to start with the letter and it can't start with a symbol.

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So I can do 'var &hello = 5'. Now I'll get en error.

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So a variable needs to start with the letter, can end in a number, that's fine.

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And there's a few other special cases. A variable can also start with a '$' or '_'.

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But we don't need to worry about that too much and the standard and JavaScript so you won't get an

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error.

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If this happens, but you do something called 'camel case'. So if it was a word, let's say 'firstname', you

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do 'camel case', because these are two separate words. You do lowercase

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the first word. Second word is going to have uppercase.

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So 'firstName'. You've capitalized the first letter and that's called 'camel case'.

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So still not getting what variables are? Well, I'm going to demonstrate this point further

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and why we need to store values in a programming language.

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I'm going to introduce you to a little cool trick called 'prompt'. And 'prompt()', when I use these brackets

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and I press 'Enter'...

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Look at that.

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I've got something here and it's asking for something and I press OK.

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And look at that!

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It returns whatever I typed.

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Let's try that again. If I go 'prompt()',

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press 'Enter' and say 'Hello', press 'OK'.

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I get that response back.

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OK.

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So how can we say something like 'What's your username?' and store that value?

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That's something that we use quite a lot on websites, right? Well, with 'prompt' you can do 'prompt()'.

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Then here we'll say "What is your username".

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So we're entering the string here.

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And if I press 'Enter'.

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OK, so it says "What is your username".

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So now if I type in my username is "andrei", I get the 'username'. So using that knowledge,

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let's make a calculator. Let's do 'var first = prompt()'

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"enter first number"

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And then I 'Enter' pressed 'Shift' here, so that I can add a new line. So 'Shift', 'Enter' and I'm going to say

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'var second = prompt()'

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"enter second number"

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Now if I press 'Enter', I'll get 'enter first number'. I'll say '5', press OK, then 'enter second number' and I

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say '10' and press OK.

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OK.

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But now I got 'undefined'.

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But here's the cool thing.

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Now I have these values held in these variables, so I can use them. If I check 'first',

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I have "5"; if I check 'second',

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I have "10".

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But you'll notice that I have double quotes [""] around them.

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And that's because 'prompt' automatically changes it to String, it's expecting a form of text.

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So there's a trick to change a String into a Number.

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And all we need to do and this is just syntax we need to remember is 'Number(first)'.

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And it'll give us '5'.

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So all we need to do now is do 'Number(first) + Number(second)'. And we'll get the sum of these 2.

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But again we can use a variable here.

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I don't want to keep typing this.

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So what if I do 'var sum = Number(first) + Number(second);'

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Press 'Enter'. Nothing yet, because it's in the 'sum' now.

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So if I asked for 'sum, I get '15'.

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OK.

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So let's write our first program here.

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I'm going to show you one other cool trick and that is 'alert'.

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So instead of 'prompt' we're going to use 'alert'. And 'alert()'.

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What it does is - it says "hi there!"

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If I press 'Enter', I get a pop-up, but without anything to enter, just an 'OK' button.

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So using this we can create a calculator.

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So let's do this.