Regular Expression Word Boundaries allow to perform "whole word only" searches within our source string.
var str = `This history is his, it is`;
The easiest way is using : \b
\b //catch the whole word; \bis // catch the ‘is‘, which in the beginning of the word is\b // catch the ‘is‘, which in the end of the word \bis\b //catch only ‘is‘, with nothing else
Catch start with ‘is‘:
var regex = /\bis/g
Catch end with ‘is‘:
var regex = /is\b/g
Catch only ‘is‘:
var regex = /\bis\b/g
Also ‘\B‘ has the oppset meanings with ‘\b‘:
\Bis // catch ‘is‘, which is NOT at the beginng is\B // catch ‘is‘, which is NOT at the end \Bis\B //catch ‘is‘, which it neither at beginng or end
Not at the begining:
var regex = /\Bis/g
Not at the end:
var regex = /is\B/g
Neither begining nor end:
var regex = /\Bis\B/g
The same effect as previous one.
[Regular Expressions] Find the Start and End of Whole Words
原文：http://www.cnblogs.com/Answer1215/p/5191609.html