Javascript Regexp And Boundaries

A colleague asked me about a Regular expression problem, and I can't seem to find and answer for him. We're using boundaries to highlight certain lengths of text in a text editor,

Solution 1:

I'm guessing it doesn't work because you need to escape the backslashes in your string that you pass to RegExp. You have this:

var rx = newRegExp('\bAlpha\b','gim');

You need this:

var rx = newRegExp('\\bAlpha\\b','gim');

The string you passed to RegExp has 2 backspace characters in it, since \b is the escape sequence for inserting a backspace into a string. You need to escape each backslash with another backslash.

Solution 2:

RegExp needs to have the escape character escaped:

newRegExp('\\bAlpha\\b')

Solution 3:

This is a string issue. \b in a string literal is a backspace!

RegExp('\\bAlpha\\b','gim'); would be the correct form

Solution 4:

There are 2 ways to write your regular expressions in Javascript

1. literal
2. RegExp object

In literal way, you use as you learned in your textbook, e.g. /balabala/ But in RegExp object, regular expression is written as a string.

Try the following codes, you know what string behaves in javascript.

alert("O\K");
alert("O\\K");

There's another occasion when Regexp written in a textarea or input box. For example,

http://www.pagecolumn.com/tool/regtest.htm

In this case, \ in Regexp need not be escaped.

Solution 5:

In fact you have to backslash everything in the string passed to the RegExp constructor :

var re = /my_([\w_]+-\d-)regexp/

is equivalent to :

var re = newRegExp("my_\(\[\\\w_\]+-\\\d-\)regexp")

And both match the following stupid example :

"my_very_obvious-4-regexp".match(re)
["my_very_obvious-4-regexp", "very_obvious-4-"]