Finding Plus Sign in Regular Expression - javascript

var string = 'abcd+1';
var pattern = 'd+1'
var reg = new RegExp(pattern,'');
alert(string.search(reg));
I found out last night that if you try and find a plus sign in a string of text with a Javascript regular expression, it fails. It will not find that pattern, even though it exists in that string. This has to be because of a special character. What's the best way to find a plus sign in a piece of text? Also, what other characters will this fail on?

Plus is a special character in regular expressions, so to express the character as data you must escape it by prefixing it with \.
var reg = /d\+1/;

\-\.\/\[\]\\ **always** need escaping
\*\+\?\)\{\}\| need escaping when **not** in a character class- [a-z*+{}()?]
But if you are unsure, it does no harm to include the escape before a non-word character you are trying to match.
A digit or letter is a word character, escaping a digit refers to a previous match, escaping a letter can match an unprintable character, like a newline (\n), tab (\t) or word boundary (\b), or a a set of characters, like any word-character (\w), any non-word character (\W).
Don't escape a letter or digit unless you mean it.

Just a note,
\ should be \\ in RegExp pattern string, RegExp("d\+1") will not work and Regexp(/d\+1/) will get error.
var string = 'abcd+1';
var pattern = 'd\\+1'
var reg = new RegExp(pattern,'');
alert(string.search(reg));
//3

You should use the escape character \ in front of the + in your pattern. eg. \+

You probably need to escape the plus sign:
var pattern = /d\+1/
The plus sign is used in regular expressions to indicate 1 or more characters in a row.

It should be var pattern = '/d\\+1/'.
The string will escape '\\' as '\' ('\\+' --> '\+') so the regex object init with /d\+1/

if you want to use + (plus sign) or $ (sigil /dollar sign), then use \ (backslash) as a prefix. Like that:
\$ or \+

Related

Java Script RegExp

var pattern = new RegExp(/[~`!#$%\^&*+=\-\[\]\\';,/{}|\\":<>\?]/);
I using RegExp to check for unavailable characters of string. How can I add the space ' ' character to that?
If you are looking for special characters, then try \W
var pattern = new RegExp(/\W/);
This will match all special characters including space.
\s for space character. See here for more info: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/RegExp

Replace the special character and space from the string in javascript

I have a below string. I need to remove all the special character and space.
var Uid = "s/Information Needed1-s84102-p306";
I tried the below code.It didn't replace the space from the string.
console.log(Uid.replace(/[^\w\s]/gi, '')}")
The output is:- sInformation Needed1s84102p306
I want the output as sInformationNeeded1s84102p306
Simply try using
/[\W_]/g
\W match any non-word character [^a-zA-Z0-9_]
Included _ if you also want to remove it then
Regex
You can just use:
console.log(Uid.replace(/\W+/g, '')}")
\W will match any non-word character including a space.
RegEx Demo
You can use this expression for your case
var x = "s/Information Needed1-s84102-p306";
console(x.replace(/[^A-Z0-9]/ig, ""));
Here is the working Link

Regexp adds invisible dot character replacing \b

I want this to be my regex: /^word\b/ (word is dynamic)
When I set it up to be dynamic I have to use this:
var word='spoon';
'spoon .table .chair'.match(new RegExp('^'+word+'\b'));
However, this finds null, while this:
var word='spoon';
'spoon .table .chair'.match(/^spoon\b/);
finds ["spoon"].
The interesting part is when I examine the difference between the regex I worte and the regex RegExp wrote:
console.log(/^spoon\b/,new RegExp('^'+word+'\b'))
It shows this:
/^spoon\b/ /^spoon/
If I then copy the second part of the log output (/^spoon/) into my code editor I see this character:
What is that? How do I do RegExp word-ending-with as I am not always guaranteed to have a space at the end when the string might be a one-word string (spoon or another word)
I'd rather just do this without the invisible thing
You've got to escape the \ in the b in the regex string by adding an extra slash:
var regex = new RegExp('^' + word + '\\b')
This is because the RegExp is expecting to see the two characters \ and b, but the string '\b' is one character, ascii 8, the backspace character (in the same way that '\n' is a single newline character).
In Javascript, \b doesn't mean a \ followed by a b. It means the backspace character (ASCII code 8). To get a \ followed by a b, you need to escape the slash so that Javascript doesn't parse it as a backspace:
'^' + word + '\\b'
The same thing applies if you want to use \d or \s or anything else: You need to escape the \ with another one so that Javascript doesn't think it's a Javascript escape code and the RegExp can parse it as what you expect.

Regular expression for validating with specific characters through javascript

I want to validate a string that does not allows the following characters.
<,>,:,","/,\,|,?,*,#
I want to validate this through JavaScript.
I was trying this with the following code.
var reg = /[^a-zA-Z0-9 \-_]+/;
reg.test(filename[0])
But this was unable to validating the symbol #.
Please help.
The problem you have is that you included the hyphen in the middle of the pattern without escaping it. This tells the engine that you are expecting a range--in this case space through underscore. It's easier (in my opinion) to place the hyphen as either the first or last character in the pattern, at which point you don't have to escape it. (It would be the second character if you are using a negated character class.)
e.g.
var reg = /[^a-zA-Z0-9 \-_]+/;
--OR--
var reg = /[^a-zA-Z0-9 _-]+/;
--OR--
var reg = /[^-a-zA-Z0-9 _]+/;
Do you only want to allow English letters a-z (and A-Z), numbers, the space, '_', and '-'? If so, that is different than disallowing the characters you specified since '☃' doesn't have the characters you provided but may not be a valid string in your use case.
In the case you just want the English alphabet, numbers, space, '_', and '-', you can use the following RegExp and conditional:
var reg = /^[a-zA-Z0-9 \-_]+$/;
if (reg.test(filename[0])) {
// String is ok
}
This says everything in the string between beginning (^) and end ($) must be one or more of the allowed characters.
If you want to disallow the characters you provided in your question, you can use:
var reg = /[\<\>\:\,\/\\\|\?\*\#]/;
if (!reg.test(filename[0])) {
// String is ok
}
This says to search for any of the characters you've listed (they are all escaped with a \ before them) and if you find any, the string is invalid. So only if the test fails is the string a valid string - that's why there's a ! before the test.
string sourceString ="something" ;
var outString = sourceString.replace(/[`~!##$%^&*()_|+\-=?;:'",.<>\{\}\[\]\\\/]/gi, '');

Regular Expression for alphabets, numbers and symbols

I am looking for a regex for allowing
Alphabets case insensitive [a-zA-Z]
hyphen and underscore [-_]
forward and backward slashes [/\\\\]
numbers [0-9]
Hence
var regex = new RegExp('^[a-zA-Z-_][/\\\\]*$');
regex.test('ABC/90-1_AB');
does not work.
Your current regexp (/^[a-zA-Z-_][/\\\\]*$/) is looking for a string that start with a letter, - or _ who are then followed by 0 or more / or \ that end the string.
Put it inside 1 bracket :
'^[-_/0-9a-zA-Z\\\\]*$'
Try:
var regex = new RegExp('[\w\\/-]','i'); // \w matches alphanumeric characters and underscore
regex.test('ABC/90-1_AB'); // returns true
JSFIDDLE
Since you aren't willing to have complex RegExp why making it difficult, when you can just match your needs with explicitly required symbols

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