[Regular Expressions] Find the Start and End of Whole Words

Regular Expression Word Boundaries allow to perform "whole word only" searches within our source string.

 Imaging we have string as follow, and we want to match all the string which start by 'is:'

var str = `This history is his, it is`;

The easiest way is using : 

  //catch the whole word;
is  // catch the 'is', which in the beginning of the word
is  // catch the 'is', which in the end of the word
is  //catch only 'is', with nothing else

Catch start with 'is':

var regex = /is/g

Catch end with 'is':

var regex = /is/g

Catch only 'is':

var regex = /is/g

Also 'B' has the oppset meanings with '':

Bis  // catch 'is', which is NOT at the beginng
isB  // catch 'is', which is NOT at the end
BisB  //catch 'is', which it neither at beginng or end

Not at the begining:

var regex = /Bis/g

Not at the end:

var regex = /isB/g

Neither begining nor end:

var regex = /BisB/g

The same effect as previous one.