JavaScript Search for Lines Beginning with a Word

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This recipe allows you to find whole words at the beginning of a line.

[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(/^Word\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 key to this expression is the line anchor metacharacter ^. You can break the expression down like this:

Regular Expression Description
^ at the start of the line, followed immediately by . . .
W then . . .
o followed by . . .
r then . . .
d and lastly . . .
\b a word boundary.

The \b character class is an anchor like the ^ line anchor. However, \b is a word anchor, and the ^ metacharacter is a line anchor.

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