Develop Reference

How can I match every sentence that contains a specific word using regex?

I am trying to highlight sentences that contain a given word. Let's say for this example that the word is "lorem". To me a sentence can end multiple ways, for example, it can end with one of the following characters: "," "!" "." "?". This can be done very easy with the following regex:
/\b((?!=|\,|\.).)+(.)\b/gim
Previous I used /^.*lorem.*?(\.|\!|\?)/gim to match sentences containing the word "lorem". But this did not work most of the time as expected. Is there any way I can use the new regex that separates sentences to only match sentences with a given word?
Just a heads up. I understand that this could be accomplished using javascript functions like replace. However, this is not an option. Our custom system, where this regex is going to be used only accepts regex as input.

You can dynamically construct your RegExp from a target string using this function:
function sentenceWith (word) {
return new RegExp(String.raw`(?:[a-z\d][^=!?,.]*?|)\b${word}\b[^=!?,.]*`, 'gi');
}
This should be like Wiktor Stribiżew's suggestion except starting matches always begin with letter or number. It assumes that the input is alphanumeric string. If the input word can contain special characters, you should sanitize it using the answer in Is there a RegExp.escape function in Javascript? before feeding it to the constructor.

How to replace matched characters with a same number of spaces

I am using javascript and looking for a regex which can replace a matched string with the same number of space. For example, I want to match a string which begins with show and ends to the end of line, this is the regex I am using /show .*$/. If users type show dbs then I want to replace with (8 spaces). How can I know the number of characters for the matched string?

I believe the most concise way to achieve such results in javascript with RegEx is to match one part of the string, replace the rest with spaces and concatenate both parts as follows:
str.replace(/^(show)(.*)/, (str, p1, p2) => p1 + p2.replace(/./g, " "));
The first replace will separate the beginning from the end and send those parts as arguments into the method. The first part can be left untouched and the second part transformed into spaces.

you can use .length on the matched element. For example
var pat = /show .*$/
'show dbs'.match(pat)[0].length
will return 8 then you can either concatenate the returned value or use .replace() on it
'show dbs'.replace(/^/, " ".repeat(8)) //we got 8 from the length property
Note: if there are multiple matches you'll have to loop over them

Split ignoring part of regex

My goal is to get the length till the nth occurrence of <br> tag in javascript so I am splitting them up.
I am trying regex
((.|\s)*?<br\s?/?>){2} //2 is the max number of lines(br tags) allowed.
While this is working fine in regexBuddy
but the string is splitted into multiple parts ignoring the <br\s?/?> part in browser.
you can view a fiddle here
What am I doing wrong

Wouldn't exec make more sense than split in this case?
var str=$('#op').html();
var match = /((.|\s)*?<br\s?\/?>){2}/i.exec(str);
if( match )
console.log(match[0].length);

The issue is that you are using the split() method, which will split the string up in to pieces based on the regular expression. This will not include your regular expression match. In your case the first section of the string matches your regular expression, so you would have an empty string at index 0 and everything after the regular expression match in index 1.
You should try to use the match() method instead, which will return an array of the pieces of the string that matched your regular expression.
var str=$('#op').html();
console.log(str.match(/(([\s\S])*?<br\s?\/?>){2}/i)[0].length);
See code.

How to replace last matched character in string using javascript

i want to replace last input character from keyboard to ''
My String Input are
sample string
"<p><strong>abscd sample text</strong></p>"
"<p>abscd sample text!</p>"
My last character is dynamic that can be any thing between
a to z, A to Z, 0 to 9, any special characters([~ / < > & ( . ] ).
So i need to replace just that character
for example in Sample 1 i need to replace "t" and in sample 2 in need to replace "!"
I tried below code. but it id not worked for me
var replace = '/'+somechar+'$/';
Any way to do it?

Step one
to replace the a character in a string, use replace() function of javaScript. Here is the MDN specification:
Returns a new string with some or all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match.
Step two
you need to location the character to be replaced through regular expression. You want to replace the last character of a string and this could be expressed as /(.+)(.)$/. . stands for any character, + means more than one character. Here (.+) matches all the character before the last one. (.) matches the last character.
What you want to replace is the one inside the second brackets. Thus you use the same string matched in the first bracket with $1 and replace whatever after it.
Here is the code to realize your intention:
text = 'abscd sample text';
text.replace(/(.+)(.)$/, '$1!');

Do you really need to use regular expressions? How about str = str.slice(0, -1); ? This will remove the last character.
If you need to replace a specific character, do it like this:
var replace = new RegExp(somechar + '$');
str = str.replace(replace, '');
You cannot use slashes in a string to construct a RegEx. This is different from PHP, for example.

I dont really understand which character you want to replace to what, but i think, you should use replace() function in JS: http://w3schools.com/jsref/jsref_replace.asp
string.replace(regexp/substr,newstring)
This means all keyboard character:
[\t\n ./<>?;:"'`!##$%^&*()[]{}_+=-|\\]
And this way you can replace all keyboard character before < mark to ""
string.replace("[a-zA-Z0-9\t\n ./<>?;:"'`!##$%^&*()[]{}_+=-|\\]<","<")

Javascript split regex question

hello I am trying what I thought would be a rather easy regex in Javascript but is giving me lots of trouble.
I want the ability to split a date via javascript splitting either by a '-','.','/' and ' '.
var date = "02-25-2010";
var myregexp2 = new RegExp("-.");
dateArray = date.split(myregexp2);
What is the correct regex for this any and all help would be great.

You need the put the characters you wish to split on in a character class, which tells the regular expression engine "any of these characters is a match". For your purposes, this would look like:
date.split(/[.,\/ -]/)
Although dashes have special meaning in character classes as a range specifier (ie [a-z] means the same as [abcdefghijklmnopqrstuvwxyz]), if you put it as the last thing in the class it is taken to mean a literal dash and does not need to be escaped.
To explain why your pattern didn't work, /-./ tells the regular expression engine to match a literal dash character followed by any character (dots are wildcard characters in regular expressions). With "02-25-2010", it would split each time "-2" is encountered, because the dash matches and the dot matches "2".

or just (anything but numbers):
date.split(/\D/);

you could just use
date.split(/-/);
or
date.split('-');

Say your string is:
let str = `word1
word2;word3,word4,word5;word7
word8,word9;word10`;
You want to split the string by the following delimiters:
Colon
Semicolon
New line
You could split the string like this:
let rawElements = str.split(new RegExp('[,;\n]', 'g'));
Finally, you may need to trim the elements in the array:
let elements = rawElements.map(element => element.trim());

Then split it on anything but numbers:
date.split(/[^0-9]/);

or just use for date strings 2015-05-20 or 2015.05.20
date.split(/\.|-/);

try this instead
date.split(/\W+/)