Develop Reference

Finding ++ in Regular Expression

I want to find ++ or -- or // or ** sign in in string can anyone help me?
var str = document.getElementById('screen').innerHTML;
var res = str.substring(0, str.length);
var patt1 = ++,--,//,**;
var result = str.match(patt1);
if (result)
{
alert("you cant do this :l");
document.getElementById('screen').innerHTML='';
}

This finds doubles of the characters by a backreference:
/([+\/*-])\1/g
[from q. comments]: i know this but when i type var patt1 = /[++]/i; code find + and ++
[++] means one arbitrary of the characters. Normally + is the qantifier "1 or more" and needs to be escaped by a leading backslash when it should be a literal, except in brackets where it does not have any special meaning.
Characters that do need to be escaped in character classes are e.g. the escape character itself (backslash), the expression delimimiter (slash), the closing bracket and the range operator (dash/minus), the latter except at the end of the character class as in my code example.
A character class [] matches one character. A quantifier, e.g. [abc]{2} would match "aa", "bb", but "ab" as well.
You can use a backreference to a match in parentheses:
/(abc)\1
Here the \1 refers to the first parentheses (abc). The entire expression would match "abcabc".
To clarify again: We could use a quantifier on the backreference:
/([+\/*-])\1{9}/g
This matches exactly 10 equal characters out of the class, the subpattern itself and 9 backreferences more.
/.../g finds all occurrences due to the modifier global (g).
test-case on regextester.com

Define your pattern like this:
var patt1 = /\+\+|--|\/\/|\*\*/;
Now it should do what you want.
More info about regular expressions: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

You can use:
/\+\+|--|\/\/|\*\*/
as your expression.
Here I have escaped the special characters by using a backslash before each (\).
I've also used .test(str) on the regular expression as all you need is a boolean (true/false) result.
See working example below:
var str = document.getElementById('screen').innerHTML;
var res = str.substring(0, str.length);
var patt1 = /\+\+|--|\/\/|\*\*/;
var result = patt1.test(res);
if (result) {
alert("you cant do this :l");
document.getElementById('screen').innerHTML = '';
}
<div id="screen">
This is some++ text
</div>

Try this:-
As
n+:- Matches any string that contains at least one n
n* Matches any string that contains zero or more occurrences of n
We need to use backslash before this special characters.
var str = document.getElementById('screen').innerHTML;
var res = str.substring(0, str.length);
var patt1 = /\+\+|--|\/\/|\*\*/;
var result = str.match(patt1);
if (result)
{
alert("you cant do this :l");
document.getElementById('screen').innerHTML='';
}
<div id="screen">2121++</div>

How to replace numbers with an empty char

i need to replace phone number in string on \n new line.
My string: Jhony Jhons,jhon#gmail.com,380967574366
I tried this:
var str = 'Jhony Jhons,jhon#gmail.com,380967574366'
var regex = /[0-9]/g;
var rec = str.trim().replace(regex, '\n').split(','); //Jhony Jhons,jhon#gmail.com,
Number replace on \n but after using e-mail extra comma is in the string need to remove it.
Finally my string should look like this:
Jhony Jhons,jhon#gmail.com\n

You can try this:
var str = 'Jhony Jhons,jhon#gmail.com,380967574366';
var regex = /,[0-9]+/g;
str.replace(regex, '\n');
The snippet above may output what you want, i.e. Jhony Jhons,jhon#gmail.com\n

There's a lot of ways to that, and this is so easy, so try this simple answer:-
var str = 'Jhony Jhons,jhon#gmail.com,380967574366';
var splitted = str.split(","); //split them by comma
splitted.pop(); //removes the last element
var rec = splitted.join() + '\n'; //join them

You need a regex to select the complete phone number and also the preceding comma. Your current regex selects each digit and replaces each one with an "\n", resulting in a lot of "\n" in the result. Also the regex does not match the comma.
Use the following regex:
var str = 'Jhony Jhons,jhon#gmail.com,380967574366'
var regex = /,[0-9]+$/;
// it replaces all consecutive digits with the condition at least one digit exists (the "[0-9]+" part)
// placed at the end of the string (the "$" part)
// and also the digits must be preceded by a comma (the "," part in the beginning);
// also no need for global flag (/g) because of the $ symbol (the end of the string) which can be matched only once
var rec = str.trim().replace(regex, '\n'); //the result will be this string: Jhony Jhons,jhon#gmail.com\n

var str = "Jhony Jhons,jhon#gmail.com,380967574366";
var result = str.replace(/,\d+/g,'\\n');
console.log(result)

Extract string between characters at the end of a URL

I have the following example url: http://example.com/this/is/the/end/
I need to extract the last piece of the url, between the last two /
There may be characters after the last / but it's always between the last two / that I need.
This is what I'm trying, I think it's pretty close but it only returns the d of end
How can I extract the full end?
Javascript
var str = 'http://example.com/this/is/the/end/';
var string = str.substring(str.lastIndexOf("/")-1,str.lastIndexOf("/"));
Here's a fiddle

Use lastIndexOf with start from index as second parameter to extract the text between the two slashes.
var str = 'http://example.com/this/is/the/end/';
var lastIndex = str.lastIndexOf('/');
var string = str.substring(str.lastIndexOf("/", lastIndex - 1) + 1, lastIndex);
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ : Get the last `/` index by starting search from `lastIndex - 1` index.
console.log(string);
You can also use string and array functions as follow.
var str = 'http://example.com/this/is/the/end/';
var string = str.split('/').slice(-2)[0];
console.log(string);
Also, regex can be used.
Regex Demo and Explanation
var str = 'http://example.com/this/is/the/end/';
var string = str.match(/\/(\w+)\/[^\/]*?$/)[1];
console.log(string);

This is a good place to use regular expressions:
Regex Live Demo
var str = 'http://example.com/this/is/the/end/';
var re = /\/([^\/]*)\/[^\/]*$/;
// \/ - look for /
// ([^\/]*) - capture zero or more characters that aren't a /
// \/ - look for last /
// [^\/]* - look for more chars that aren't /
// $ - match the end of the string
var last = re.exec(str)[1];
console.log(last); //end

You can simply split and slice
'http://example.com/this/is/the/end/'.split('/').slice(-2)[0]

JS - Split string into substrings by regex

Let's say I have a string that starts by 7878 and ends by 0d0a or 0D0A such as:
var string = "78780d0101234567890123450016efe20d0a";
var string2 = "78780d0101234567890123450016efe20d0a78780d0103588990504943870016efe20d0a";
var string 3 = "78780d0101234567890123450016efe20d0a78780d0103588990504943870016efe20d0a78780d0101234567890123450016efe20d0a"
How can I split it by regex so it becomes an array like:
['78780d0101234567890123450016efe20d0a']
['78780d0101234567890123450016efe20d0a','78780d0101234567890123450016efe20d0a']
['78780d0101234567890123450016efe20d0a','78780d0101234567890123450016efe20d0a','78780d0101234567890123450016efe20d0a']

You can split the string with a positive lookahead (?=7878). The regex isn't consuming any characters, so 7878 will be part of the string.
var rgx = /(?=7878)/;
console.log(string1.split(rgx));
console.log(string2.split(rgx));
console.log(string3.split(rgx));
Another option is to split on '7878' and then take all the elements except first and add '7878' to each of them. For example:
var arr = string3.split('7878').slice(1).map(function(str){
return '7878' + str;
});
That works BUT it also matches strings that do NOT end on 0d0a. How
can I only matches those ending on 0d0a OR 0D0A?
Well, then you can use String.match with a plain regex.
console.log(string3.match(/7878.*?0d0a/ig));

Javascript split by spaces but not those in quotes

The goal is to split a string at the spaces but not split the text data that is in quotes or separate that from the adjacent text.
The input is effectively a string that contains a list of value pairs. If the value value contains a space it is enclosed in quotes. I need a function that returns an array of value-pair elements as per the example below:
Example Input:
'a:0 b:1 moo:"foo bar" c:2'
Expected result:
a:0,b:1,moo:foo bar,c:2 (An array of length 4)
I have checked through a load of other questions but none of them (I found) seem to cope with my issue. Most seem to split at the space within the quotes or they split the 'moo:' and 'foo bar' into separate parts.
Any assistance would be greatly appreciated,
Craig

You can use this regex for split:
var s = 'a:0 b:1 moo:"foo bar" c:2';
var m = s.split(/ +(?=(?:(?:[^"]*"){2})*[^"]*$)/g);
//=> [a:0, b:1, moo:"foo bar", c:2]
RegEx Demo
It splits on spaces only if it is outside quotes by using a positive lookahead that makes sure there are even number of quotes after a space.

You could approach it slightly differently and use a Regular Expression to split where spaces are followed by word characters and a colon (rather than a space that's not in a quoted part):
var str = 'a:0 b:1 moo:"foo bar" c:2',
arr = str.split(/ +(?=[\w]+\:)/g);
/* [a:0, b:1, moo:"foo bar", c:2] */
Demo jsFiddle
What's this Regex doing?
It looks for a literal match on the space character, then uses a Positive Lookahead to assert that the next part can be matched:
[\w]+ = match any word character [a-zA-Z0-9_] between one and unlimited times.
\: = match the : character once (backslash escaped).
g = global modifier - don't return on first match.
Demo Regex101 (with explanation)

Any special reason it has to be a regexp?
var str = 'a:0 b:1 moo:"foo bar" c:2';
var parts = [];
var currentPart = "";
var isInQuotes= false;
for (var i = 0; i < str.length, i++) {
var char = str.charAt(i);
if (char === " " && !isInQuotes) {
parts.push(currentPart);
currentPart = "";
} else {
currentPart += char;
}
if (char === '"') {
isInQuotes = !isInQuotes;
}
}
if (currentPart) parts.push(currentPart);