Word boundary: \b

A word boundary pattern:\b is a test, just like pattern:^ and pattern:$. When the regexp engine (program module that implements searching for regexps) comes across pattern:\b, it checks that the position in the string is a word boundary. There are three different positions that qualify as word boundaries: - At string start, if the first string character is a word character pattern:\w. - Between two characters in the string, where one is a word character pattern:\w and the other is not. - At string end, if the last string character is a word character pattern:\w. For instance, regexp pattern:\bJava\b will be found in subject:Hello, Java!, where subject:Java is a standalone word, but not in subject:Hello, JavaScript!. In the string subject:Hello, Java! following positions correspond to pattern:\b: So, it matches the pattern pattern:\bHello\b, because: 1. At the beginning of the string matches the first test pattern:\b. 2. Then matches the word pattern:Hello. 3. Then the test pattern:\b matches again, as we’re between subject:o and a comma. So the pattern pattern:\bHello\b would match, but not pattern:\bHell\b (because there’s no word boundary after l) and not Java!\b (because the exclamation sign is not a wordly character pattern:\w, so there’s no word boundary after it). We can use pattern:\b not only with words, but with digits as well. For example, the pattern pattern:\b\d\d\b looks for standalone 2-digit numbers. In other words, it looks for 2-digit numbers that are surrounded by characters different from pattern:\w, such as spaces or punctuation (or text start/end).

alert( "Hello, Java!".match(/\bJava\b/) ); // Java
alert( "Hello, JavaScript!".match(/\bJava\b/) ); // null