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Now building up on what we learned

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in the last lecture about storing Booleans

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and having checks like this,

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there is another important concept in JavaScript,

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which you don't find in most programming languages,

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but which is a key part of JavaScript,

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and which you therefore also have to know.

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Let's say we have a constant,

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or a variable, doesn't matter,

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"enteredUserName",

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and that could be Maximilian.

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It does not matter.

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Now let's assume this is again a value

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which we actually fetch from some input field,

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just like we do it in demo.js.

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There, we also get some entered value.

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Let's assume the same is the case here

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for "enteredUserName."

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Now we might have some code that should only execute

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if this is a non empty string.

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And then, we could say, "Input is valid."

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So, we could check if this is a non empty string,

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if it has a more than zero characters.

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Now for that, we can write "enteredUserName"

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and get the length of that string with the length property

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and check if that's greater than zero.

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And if it is, which it in this case is,

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then I can save this and I get, "Input is valid."

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But, if that's all we care about,

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there is a even shorter way of checking this.

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We can also write "if enteredUserName," like that.

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And if I save that, I also get, "Input is valid."

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And if I go back and I turn this into an empty string,

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so no input was provided,

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then I actually don't get this output.

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So this also works as we would want it to work.

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But why?

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Because JavaScript has this concept of

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truthy and falsy values.

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Now, we have true and false for Booleans,

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but in a place where JavaScript wants a Boolean,

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like in this if condition here,

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if you provide a non-Boolean value,

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JavaScript will basically try to convert

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that provided value to a Boolean,

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and it has certain rules for that conversion.

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Now I got dedicated deep dive courses

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where I dive way deeper into all the niche details

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of how JavaScript does this conversion

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and I dive into all the tricky cases

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where this conversion might be strange,

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but it's generally straightforward.

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An empty string, or the number zero,

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will be treated as false.

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A string with zero inside of it

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would not be treated as false

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since this is not an empty string.

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So empty string or zero are basically treated like false.

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A string with anything in there,

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even if it's the text "false,"

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would be treated as true because it's not empty.

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So it's really only the question of

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whether it's empty or not that matters.

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Even a blank character would count as not empty

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and therefore as true.

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And hence, if you use a string or a number here,

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then this will be treated as true,

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if it's not empty or not zero,

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and it will be treated as false

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if it is an empty string or a zero number.

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And that's why this check also works.

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This might sound like a niche case,

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but it actually isn't.

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Very often you will perform checks like this

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simply because it's shorter

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than checking for length greater than zero,

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and it has exactly the same result.

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So whilst you could do that,

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this is simply shorter

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and it works because of this truthy falsy behavior

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that's built into JavaScript.

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Now, if that's still a bit much

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and a bit confusing at this point,

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again, don't worry.

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We'll have many examples throughout this course,

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but as we are talking about if statements

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and Booleans right now,

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that's definitely all of the concept

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that needed to be introduced at this point.