If you recall when we changed the text in the span tag, we had to put the JavaScript script at the bottom so that it wouldn't give us an error.
What if we wanted to make it so that the JavaScript code didn't run automatically. Insert functions. You have seen them already. You used them with alert, log, write, getElementById. Now we are going to create one ourselves.
Functions look like this.
function myFunction()
{
window.alert("Hi there!");
}
We just created a function called myFunction, and it contains one line of code, which just so happens to be another window.alert. However, it will not run unless we call myFunction somewhere.
You might notice that there are {} before and after the window.alert. These indicate where the function body begins and ends. Without them, the function doesn't work.
What does this look like on a full page?
<html>
<title>Functions</title>
<head>
<script>
function displayFavoriteColor()
{
var favoriteColor = "blue";
document.getElementById("myTag").innerHTML = "Favorite Color " + favoriteColor;
}
</script>
</head>
<body>
<span id="myTag">This is my favorite text</span>
</body>
</html>
Not calling the function, results in the original text shown. How do we call this function? Below is one way.
<html>
<title>Functions</title>
<head>
<script>
function displayFavoriteColor()
{
var favoriteColor = "blue";
document.getElementById("myTag").innerHTML = "Favorite Color " + favoriteColor;
}
</script>
</head>
<body onload="displayFavoriteColor();">
<span id="myTag">This is my favorite text</span>
</body>
</html>
Placing the function name in the onload event of the body is one way to call the function. This event is just a unique attribute of the body and allows us to call JavaScript functions. Neat huh?
Now the text should be changed right when you open the page.
What about parameters?
An example of calling parameters looks like this.
<html>
<title>Functions</title>
<head>
<script>
function displayFavoriteColor(color)
{
var favoriteColor = color;
document.getElementById("myTag").innerHTML = "My favorite color is " + favoriteColor;
}
</script>
</head>
<body onload="displayFavoriteColor('blue');">
<span id="myTag">This is my favorite text</span>
</body>
</html>
We declare the variable in the displayFavoriteColor function. It is called color. Then, we assign that variable to the favoriteColor variable in the function. Then, in the onload event, we pass in a value. In this case, we pass in a value of blue inside of single quotes. We do this because the onload puts the function call inside of double-quotes.
What about getting information from a form or something like that? Move on, and you will find out!