RegExp Boundaries

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  • turned_in_notBoundaries
    • ^x
    • x$
    • \b
    • \B
  • To run below examples, try it inside <script> tag, in a basic html file

^x

It matches x at the beginning of whole string & if 'm' flag is used then matches x at the beginning of first line, if 'mg' flag used then matches x at the beginning of every line

For example : 

var str="good morning
my friend";
var pattern=/^../mg;
alert(str.match(pattern));
// Output: go,my

Matches:
good morning
my friend

Comment : Check first 2 letters of every line in string


x$

It matches x at the end of whole string & if 'm' flag is used then matches x at the end of first line, if 'mg' flag used then matches x at the end of every line

For example : 

var str="good morning
my friend";
var pattern=/..$/mg;
alert(str.match(pattern));
// Output: ng,nd

Matches:
good morning
my friend

Comment : Check last 2 letters of every line in string


\b

It matches only if, before/after of x is not of the same type '\w' = [0-9a-ZA-Z_] or '\W' = [^0-9a-ZA-Z_]

\bx : x can be any \w or \W where letter just before x is not of the same type \w or \W
x\b : x can be any \w or \W where letter just after x is not of the same type \w or \W

Example for \bx: 

var str="goood food today";
var pattern=/[gft]o/g;
alert(str.match(pattern));
// Output: go,fo,to

Matches: goood food today

Comment : Check letter just before go,fo,to in the string, it's not of the same type \w

Example for x\b: 

var str="goood food+ today";
var pattern=/.[dy]/g;
alert(str.match(pattern));
// Output: od,od,ay

Matches: good food+ today

Comment : Check letter just after od,od,ay in the string, it's not of the same type \w


\B

It matches only if, before/after of x is of the same type '\w' = [0-9a-ZA-Z_] or '\W' = [^0-9a-ZA-Z_]

\Bx : x can be any \w or \W where letter just before x is of same type \w or \W
x\B : x can be any \w or \W where letter just after x is of same type \w or \W

Example for \Bx: 

var str="books are good friend";
var pattern=/Boo./g;
alert(str.match(pattern));
// Output: ook,ood

Matches: books are good friend

Comment : Check letter just before ook & ood in the string, it's of same type \w

Example for x\B: 

var str="books are good friend";
var pattern=/oo.B/g;
alert(str.match(pattern));
// Output: ook

Matches: books are good friend

Comment : Check letter just after ook in the string, it's of same type \w



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