Validating an email field includes checking to make sure there are no illegal characters, like spaces, and that all the essentials of a legal email address are there: one or more characters, followed by @, followed by one or more characters, followed by a dot, followed by two to four characters. The standard way to test for all this is to match the user's entry with a regular expression. Regular expressions are beyond the scope of this book, but I'll give you a taste of them at the end of the chapter. Meanwhile, here's how to head off many user errors by
using indexOf.
Let's start by checking for spaces, which are illegal in an email address.
JavaScript:
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| function validateEmail() {
var eEntered = document.getElementByld("email").value;
if (eEntered.indexOf(" ") !== -1) {
alert("No spaces allowed in address");
return false;
}
} |
Line 3 is the key here. If the index of the illegal space character is anything other than -1, it means the character is in there somewhere, and an alert displays.
If you wanted to, you could test for the presence of all the other illegal characters the same way. But in that case, you'd be better off using a regular expression, as I show at the end of this chapter.
In an email address you want to see the @ sign at least one character from the beginning of the string and no closer to the end of the string than 5 characters away. Here's a line that adds this test to the example function.
JavaScript:
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| function validateEmail() {
var addressIsLegal = true;
var eEntered = document.getElementByld("address").value;
if (eEntered.indexOf(" ") !== -1) {
addressIsLegal = false;
}
if (eEntered.indexOf("@") < 1 || eEntered.indexOf ("@") > eEntered.length - 5) {
addressIsLegal = false;
}
if (addressIsLegal === false) {
alert("Please correct email address");
return false;
}
} |
About line 7: The first part, left of the pipes, tests whether the character is at the beginning of the address, which would be illegal. The second part, right of the pipes, tests whether there are fewer than 4 characters following the character. Since there must be at least one character for the domain name plus a dot plus at least two characters for the extension, fewer than 4 characters following the @ would be illegal.
Finally, I'll add a test for the dot that needs to be at least 1 character away from the and have 2 to 4 characters following it.
JavaScript:
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| function validateEmail() {
var addressIsLegal = true;
var eEntered = document.getElementByld("address").value;
if (eEntered.indexOf(" ") !== -1) {
addressIsLegal = false;
}
if (eEntered.indexOf("@") < 1 || eEntered.indexOf("@") > eEntered.length - 5) {
addressIsLegal = false;
}
if (eEntered.indexOf(".") - eEntered.indexOf("@") < 2 || eEntered.indexOf(".") > eEntered.length - 3) {
addressIsLegal = false;
}
if (addressIsLegal === false) {
alert("Please correct email address");
return false;
}
} |
Line 10: There must be at least one character between the dot and the @. The first part, left of the pipes, tests whether that one character (or more) is missing, which would be illegal. There must also be at least 2 characters following the dot. The second part, right of the pipes, tests whether there are fewer than 2 characters following the character, which would be illegal.
:strip_icc():strip_exif()/u/43400/avatar.jpeg?f=community){kind=avatar}
Vervolgens doen ze wat truukjes of te kijken of (wat ik vermoed) een e-mailadres "geldig" is (volgens hun definitie van "geldig" dan).:strip_exif()/u/383015/crop5b892183362a8.gif?f=community)
.:strip_icc():strip_exif()/u/195618/mp3smiley.jpg?f=community)
:fill(white):strip_exif()/f/image/FT5Z4FOE2BNXMr8umvWvBhxv.png?f=user_large)
Los van de ranzige (en overigens 
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