Develop Reference

How do I pass a variable into regex with Node js?

So basically, I have a regular expression which is
var regex1 = /10661\" class=\"fauxBlockLink-linkRow u-concealed\">([\s\S]*?)<\/a>/;
var result=text.match(regex1);
user_activity = result[1].replace(/\s/g, "")
console.log(user_activity);
What I'm trying to do is this
var number = 1234;
var regex1 = /${number}\" class=\"fauxBlockLink-linkRow u-concealed\">([\s\S]*?)<\/a>/;
but it is not working, and when I tried with RegExp, I kept getting errors.

You can use RegExp to create regexp from a string and use variables in that string.
var number = 1234;
var regex1 = new RegExp(`${number}aa`);
console.log("1234aa".match(regex1));

You can build the regex string with templates and/or string addition and then pass it to the RegExp constructor. One key in doing that is to get the escaping correct as you need an extra level of escaping for backslashes because the interpretation of the string takes one level of backslash, but you need one to survive as it gets to the RegExp contructor. Here's a working example:
function match(number, str) {
let r = new RegExp(`${number}" class="fauxBlockLink-linkRow u-concealed">([\\s\\S]*?)<\\/a>`);
return str.match(r);
}
const exampleHTML = 'Some link text';
console.log(match(1234, exampleHTML));
Note, using regex to match HTML like this becomes very order-sensitive (whereas the HTML itself isn't order-sensitive). And, your regex requires exactly one space between classes which HTML doesn't. If the class names were in a slightly different order or spacing different in the <a> tag, then it would not match. Depending upon what you're really trying to do, there may be better ways to parse and use the HTML that isn't order-sensitive.

I solved it with the method of Adem,
function escapeRegExp(string) {
return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
}
var number = 1234;
var firstPart = `<a href="/forum/search/member?user_id=${number}" class="fauxBlockLink-linkRow u-concealed">`
var regexpString = escapeRegExp(firstPart) + '([\\s\\S]*?)' + escapeRegExp('</a>');
console.log(regexpString)
var sample = ` `
var regex1 = new RegExp(regexpString);
console.log(sample.match(regex1));
in the first place the issue was actually the way I was reading the file, the data I was applying the match on, was undefined.

How to get an exact string in javascript

I am trying to get a Substring from a string.
Here is the slice from the code:
var inputString = '[app:abcd][class:sample][instance:value:wq-23333:site-
1.1.1.1:jhk-1][descr:endss.]'
I want to get the value after instance: to the next closing of square bracket.
So the output should be :
var outputString = 'value:wq-23333:site-1.1.1.1:jhk-1'
Note : The position where the string instance comes is not fixed and the above is a String not an Array and I am writing code in javascript.

Assuming you do have a string and just forgot to add quotes you could use a regexp /\[instance\:([^\]]+)\]/ that looks for [instance: part and captures everything until next closing bracket.
var inputString = "[app:abcd][class:sample][instance:value:wq-23333:site-1.1.1.1:jhk-1][descr:endss.]"
console.log(/\[instance\:([^\]]+)\]/.exec(inputString)[1])

How to ignore escape characters in javascript?

I have the following string:
var str = '\x27';
I have no control on it, so I cannot write it as '\\x27' for example. Whenever I print it, i get:
'
since 27 is the apostrophe. When I call .length on it, it gives me 1. This is of course correct, but how can I treat it like a not escaped string and have it print literally
\x27
and give me a length of 4?

I'm not sure if you should do what you are trying to do, but this is how it works:
var s = '\x27';
var sEncoded = '\\x' + s.charCodeAt(0).toString(16);
s is a string that contains one character, the apostrophe. The character code as a hexadecimal number is 27.

After the assignment var str = '\x27';, you can't tell where the contents of str came from. There's no way to find out whether a string literal was assigned, or whether the string literal contained an escape sequence. All you have is a string containing a single apostrophe character (Unicode code point U+0027). The original assignment could have been
var str = '\x27'; // or
var str = "'"; // or
var str = String.fromCodePoint(3 * 13);
There's simply no way to tell.
That said, your question looks like an XY problem. Why are you trying to print \x27 in the first place?

Simple Javascript string manipulation

I have a string that will look something like this:
I'm sorry the code "codehere" is not valid
I need to get the value inside the quotes inside the string. So essentially I need to get the codehere and store it in a variable.
After some researching it looks like I could loop through the string and use .charAt(i) to find the quotes and then pull the string out one character at a time in between the quotes.
However I feel there has to be a simpler solution for this out there. Any input would be appreciated. Thanks!

You could use indexOf and lastIndexOf to get the position of the quotes:
var openQuote = myString.indexOf('"'),
closeQuote = myString.lastIndexOf('"');
Then you can validate they are not the same position, and use substring to retrieve the code:
var code = myString.substring(openQuote, closeQuote + 1);

Regex:
var a = "I'm sorry the code \"codehere\" is not valid";
var m = a.match(/"[^"]*"/ig);
alert(m[0]);

Try this:
var str = "I'm sorry the code \"cod\"eh\"ere\" is not valid";
alert(str.replace(/^[^"]*"(.*)".*$/g, "$1"));

You could use Javascript's match function. It takes as parameter, a regular expression. Eg:
/\".*\"/

Use regular expressions! You can find a match using a simple regular expressions like /"(.+)"/ with the Javascript RegExp() object. Fore more info see w3schools.com.

Try this:
var msg = "I'm sorry the code \"codehere\" is not valid";
var matchedContent = msg.match(/\".*\"/ig);
//matchedContent is an array
alert(matchedContent[0]);

You should use a Regular Expression. This is a text pattern matcher that is built into the javascript language. Regular expressions look like this: /thing to match/flags* for example, /"(.*)"/, which matches everything between a set of quotes.
Beware, regular expressions are limited -- they can't match nested things, so if the value inside quotes contains quotes itself, you'll end up with a big ugly mess.
*: or new RegExp(...), but use the literal syntax; it's better.

You could always use the .split() string function:
var mystring = 'I\'m sorry the code "codehere" is not valid' ;
var tokens = [] ;
var strsplit = mystring.split('\"') ;
for(var i=0;i<strsplit.length;i++) {
if((i % 2)==0) continue; // Ignore strings outside the quotes
tokens.push(strsplit[i]) ; // Store strings inside quotes.
}
// Output:
// tokens[0] = 'codehere' ;

Splitting string in javascript

How can I split the following string?
var str = "test":"abc","test1":"hello,hi","test2":"hello,hi,there";
If I use str.split(",") then I won't be able to get strings which contain commas.
Whats the best way to split the above string?

I assume it's actually:
var str = '"test":"abc","test1":"hello,hi","test2":"hello,hi,there"';
because otherwise it wouldn't even be valid JavaScript.
If I had a string like this I would parse it as an incomplete JSON which it seems to be:
var obj = JSON.parse('{'+str+'}');
and then use is as a plain object:
alert(obj.test1); // says: hello,hi
See DEMO
Update 1: Looking at other answers I wonder whether it's only me who sees it as invalid JavaScript?
Update 2: Also, is it only me who sees it as a JSON without curly braces?

Though not clear with your input. Here is what I can suggest.
str.split('","');
and then append the double quotes to each string

str.split('","'); Difficult to say given the formatting
if Zed is right though you can do this (assuming the opening and closing {)
str = eval(str);
var test = str.test; // Returns abc
var test1 = str.test1; // returns hello,hi
//etc

That's a general problem in all languages: if the items you need contain the delimiter, it gets complicated.
The simplest way would be to make sure the delimiter is unique. If you can't do that, you will probably have to iterate over the quoted Strings manually, something like this:
var arr = [];
var result = text.match(/"([^"]*"/g);
for (i in result) {
arr.push(i);
}

Iterate once over the string and replace commas(,) following a (") and followed by a (") with a (%) or something not likely to find in your little strings. Then split by (%) or whatever you chose.