front-end-developer_1_

Front-End-Developer - Level 1
type $("input#age").val(); in the JavaScript console to see for yourself). An empty string
isn't true or false .
What's happening here is that JavaScript has concepts called truthy and falsey . Falsey
values include empty strings, the number 0 , the number NaN , undefined , null (which
we still haven't seen), and, of course, false itself. If JavaScript sees any of these as a
branching condition, it will treat them as false. Everything else is truthy.
Here's another operator you should know about: if you want to test that something is not
true, you can use the ! (not) operator like this:
if (!under18) {
}
// do something only adults can do
And finally, here's a trick you'll commonly see. This code:
if (something > 0) {
return true;
} else {
return false;
}
can be written simply as:
return something > 0;
That's because the condition ( something > 0 ) evaluates to a boolean - either true or false.
So we can just return that Boolean.
Summary
Logical operators:
&& means and: gender === 'male' && age < 26
|| means or: gender === 'male' || age < 26
! means not: !under18 Empty strings, the number 0 , the number NaN , undefined ,
null , and false itself are falsey. If JavaScript sees any of these as a branching
condition, it will treat them as false. Everything else is truthy.
More Branching
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