JavaScript Search for Repeated Words
From Regex Regular Expression Encyclopedia
You can use this recipe to find words that appear more than once on a line, such as the the.
[edit] code
<html>
<head>
<title></title>
</head>
<body>
<form name="form1">
<input type="textbox" name="txtInput" />
<script type="text/javascript">
function validate() {
if (! document.form1.txtInput.value.match(/\b(\w+)\s\1\b/)) {
alert("Please enter valid value!")
} else {
alert("Success!")
}
}
</script>
<input type="button" name="btnSubmit" onclick="validate()" value="Go" />
</form>
</body>
</html>[edit] How It Works
The most important aspect of this regular expression is the back reference, which is \1 in all the previous recipes. The back reference is just a way of saying “whatever you found in the first group.” The parentheses in the expression define the group. Here’s a breakdown of the expression:
| Regular Expression | Description |
|---|---|
| \b | is a word boundary, followed by . . . |
| (...) | a group (explained next), then . . . |
| \s | a space . . . |
| + | one or more times, then . . . |
| \1 | whatever was found in the group, and lastly . . . |
| \b | a word boundary. |
| The group is simply (\w+), which is as follows: | |
| \w | a word character . . . |
| + | found one or more times. |
This will match a word. The expression begins and ends with a word boundary anchor. This is to prevent the expression from matching a string such as quarterback backrub. If the word boundary anchors are removed, the expression will start matching subsections of words.
