- Create Functions Using Arrow Syntax 4:34
- Concise Arrow Function Syntax
- Arrow Functions Review 5 questions
- Default Function Parameters 5:11
- Create an Arrow Function 1 objective
- Descriptive Comments for Functions
- Function Challenge 1:24
- Function Challenge Solution 4:28
- Testing for Number Arguments 4:02
- JavaScript Functions Review 6 questions
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Create Functions Using Arrow Syntax
4:34Learn how arrow functions provide a special, more concise syntax for creating functions. Arrow functions are similar to function expressions; they're appropriately called "arrow function expressions."
[MUSIC]
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As you learn more about JavaScript and
how the language evolves, you'll realize
0:04
that it provides different and perhaps
more efficient ways to do similar things.
0:08
Working with functions
is one of those things.
0:12
So far you've learned how to write
a function as a declaration and
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as an expression.
0:19
A function declaration, for example,
defines a function using the function
0:20
keyword followed by
the name of the function.
0:24
And a function expression
is an anonymous function or
0:26
a function without a name
that's assigned to a variable.
0:30
In this stage, I'll teach you another
method for writing functions.
0:33
You'll learn how arrow functions provide
a special more concise syntax for
0:37
creating functions.
0:41
Arrow functions are very similar
to function expressions.
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In fact, they're properly called Arrow
Function Expressions, the basic syntax for
0:45
an arrow function looks like this.
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You omit the function keyword [SOUND] and
after the parentheses add the arrow token,
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which is just an equals sign immediately
followed by the greater than sign.
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The body of the function can remain
the same but as you'll soon learn,
1:01
there are ways to make error
functions even more compact.
1:05
You can access the new set of files by
launching the work space with this video.
1:08
Open the file arrow-functions.js
located inside the js folder.
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The files are already
linked to index dot html.
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The get randomNumber function in this file
is written as a function declaration.
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That's a function that begins
with the function key word,
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followed by the name of the function and
a pair of parentheses.
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We're going to convert this
function to an arrow function.
1:30
Now, arrow functions are similar to
the function expressions you learned about
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earlier.
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So let's first change the getRandomNumber() function declaration to
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a function expression and
then to an arrow function.
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Create a variable named getRandomNumber
and assign an anonymous function to it.
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You can make this function even more
concise using the arrow function syntax.
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To convert the getRandomNumber function
expression to an arrow function,
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remove the function keyword.
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And after the parenthesis add an arrow,
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which is an equal sign immediately
followed by a greater than sign.
2:09
All right, so now we've rewritten the
function assigned to the getRandomNumber
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variable as an arrow function.
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And notice how arrow functions
themselves are anonymous functions,
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because they don't have a name,
and you call or
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reference the function
using the variable name.
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Let's test the function by calling
it in the JavaScript console.
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And it works,
we get a random number between 1 and 6.
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Keep in mind that arrow functions
mostly behave like function expression.
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For example, arrow function
expressions are not hoisted or
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lifted up to the top of their
scope by the JavaScript engine.
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They'd load only when the JavaScript
engine reaches the line of code their on.
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So if you tried to call an arrow
function expression before it's defined,
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you'll get an error.
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Now currently,
this arrow function has no parameters.
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When you need to add parameters
to the function definition,
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you include them just as you do in
function declarations and expressions.
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For example, add an upper
parameter inside the parentheses,
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then use the value of the upper
parameter inside the function.
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I'll save my file and
test it in the console.
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By calling getRandomNumber() and
passing it the argument 12, and
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there's my random number.
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Besides being concise,
the arrow syntax has other benefits and
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help solve common JavaScript problems and
gotchas.
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Like other features,
they have advantages and disadvantages,
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which are beyond the scope of this course.
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But you'll get to know about
them later as you learn more and
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more about the details of JavaScript.
3:44
And keep in mind that arrow functions
are not meant to replace regular function
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declarations or function expressions.
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It's just a newer syntax for
writing functions.
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Function declarations, for example,
are still widely used by developers.
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They're useful because they work in
a slightly different way than arrow
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functions.
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For instance, function declarations
are hoisted while arrow functions are not.
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There are specific places where arrow
functions can improve your code too.
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For example, in future lessons,
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you'll experience the advantages of
the short arrow function syntax.
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When you learn to pass functions as
arguments to other functions with
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what are called callbacks, all right?
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Now, to get additional practice
writing arrow functions,
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why don't you rewrite this getArea
function declaration you wrote earlier as
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an arrow function expression.
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You can check out the solution in
the teacher's notes with this video.
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