JavaScript—An Object Based Language - Beginning JavaScript - page 108

var myString = "Welcome to Wrox topics. " +
"The Wrox website is www.wrox.com. " +
"Visit the Wrox website today. Thanks for buying Wrox";
var foundAtPosition = 0;
var wroxCount = 0;
while (foundAtPosition != -1) {
foundAtPosition = myString.indexOf("Wrox", foundAtPosition);
if (foundAtPosition != -1) {
wroxCount++;
foundAtPosition++;
}
}
document.write("There are " + wroxCount + " occurrences of the word Wrox");
</script>
</body>
</html>
Save this example as ch5 _ example1.html . When you load the page into your browser, you should see
the following sentence: There are 4 occurrences of the word Wrox.
At the top of the script block, you built up a string inside the variable myString , which you then want
to search for the occurrence of the word Wrox . You also define two variables: wroxCount will contain
the number of times Wrox is found in the string, and foundAtPosition will contain the position in the
string of the current occurrence of the substring Wrox .
You then used a while loop, which continues looping all the while you are finding the word Wrox in the
string—that is, while the variable foundAtPosition is not equal to ‐1 . Inside the while loop, you have
this line:
foundAtPosition = myString.indexOf("Wrox", foundAtPosition);
Here you search for the next occurrence of the substring Wrox in the string myString . How do you
make sure that you get the next occurrence? You use the variable foundAtPosition to give you the
starting position of your search, because this contains the index after the index position of the last
occurrence of the substring Wrox . You assign the variable foundAtPosition to the result of your
search, the index position of the next occurrence of the substring Wrox .
Each time Wrox is found (that is, each time foundAtPosition is not ‐1 ) you increase the variable
wroxCount , which counts how many times you have found the substring, and you increase
foundAtPosition so that you continue the search at the next position in the string:
if (foundAtPosition != -1) {
wroxCount++;
foundAtPosition++;
}
Finally, you document.write() the value of the variable wroxCount to the page.