JavaScript Core Objects - JavaScript by Example - page 255

EXAMPLE 9.27 ( CONTINUED )

2 while( email_addr.indexOf("@") == -1 ){

3 alert( "Invalid email address.");

email_addr=prompt("What is your email address? ","");

}
document.write("<br />OK.<br />");
</script>
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</font>
</body>
</html>

EXPLANATION
1

The user is prompted for his or her e-mail address and the input is assigned to a
string called email_addr .

2 The loop expression uses the indexOf() String method to see if there is an @ sym-

bol in the e-mail address. If there isn't, the indexOf() method returns -1 and the
body of the loop is executed.

3 If the indexOf() method didn't find the @ substring, the alert box appears and the

user is prompted again (see Figures 9.31 and 9.32). The loop terminates when the
user enters an e-mail address containing an @ sign. Of course, this is just a simple
test for validating an e-mail address; more elaborate methods of validation are dis-
cussed in Chapter 17, “Regular Expressions and Pattern Matching.”

Figure 9.31 Using the indexOf() String method.

Figure 9.32 The user entered an e-mail address without the @ symbol.