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Regex to extract arguments passed into string '#substr( , , )'

we have a text input where the user can enter some text and apply some functions on top of the text like ( substr , replace ) etc. For example user can enter the text "hello" in the text input and can apply the substring function ( #substr(hello, 'startIndex', 'length'))and can mention the start index and the length etc.
Need to use the regex to extract the values passed into the #substr function for validating the mandatory fields. For example 'start index' and 'length' is required when the user selects the substr function.
Below are the different scenarios and its expected output .
#substr(hello,1,3) ---> ['hello','1','3']
#substr($(sometext),1,3) ---> ['$(sometext)','1','3']
#substr(#trim(hello),1,3) ----> ['#trim(hello)','1','3']
#substr(#replace(hello-world,hello,hi),1,3) ---> ['#replace(hello-world,hello,hi)','1','3']
As from the above examples need to extract the arguments passed into the #substr function as array elements.
Tried this regex
/#substr\((.*?),(.*?),(.*?)\)/g
This fails when we have a nested functions like this - #substr(#replace(hello-world,hello,hi),1,3)

You could use the below regex with capturing groups.
#(\S+?)\((.*)\,(\d+),(\d+)\)
For nested matching, it is not impossible, but much complex in regex. The easy approach should be avoiding regex and using js code for nested matching.

This regex can solve your problems, if the string takes up an entire line, but if you enter comma commands in the second argument, it will fail, this is a very complex problem to solve with simple regex. I think you're knocking on the compilers' door.
regex = /^#substr\((.*),(.*),(.*)\)$/;
text = "#substr(#replace(hello-world,hello,hi),1,3)";
console.log(regex.exec(text));

If you're trying to get the length of user input or index, you could put all the desired methods inside a function or multiple functions that call be called on button-click.
https://www.bitdegree.org/learn/javascript-input
I may be misunderstanding but if I take one of your examples:
#substr(hello,1,3) ---> ['hello','1','3']
When I run
str = "hello world"
str.substring(1,3) --> I get "el" (not "hello", "1", "3")
Get some text:
var firstName = document.getElementById("firstName").value;
var age = document.getElementById("age").value;
Click a button to call your function.
function doSubstringStuff(textValue, subString_mode) {
if subString_mode == "length" {
return textValue.length;
}
OR
Validate the length matches your criteria.
if (textValue.length > 10) {
alert("The name must have no more than 10 characters");
Or Perform other tasks, determined by the argument "mode"
else if subString_mode == "integer_test"{
if (isNaN(textValue) || age < 12 || age > 100){alert("The age must be between numbers 12 and 100")};

How to get a value from page source code from a function tag?

here is the function from the source code
function dosubmit()
{
if (getObj("Frm_Username").value == "")
{
getObj("errmsg").innerHTML = "Username cannot be empty.";
getObj("myLayer").style.visibility = "visible" ;
return;
}
else
{
getObj("LoginId").disabled = true;
getObj("Frm_Logintoken").value = "3";
document.fLogin.submit();
}
}
i want to get the value of getObj("Frm_Logintoken") as i can't pull the value
from #Frm_Logintoken
using document.getElementById("#Frm_Logintoken") this gives me null
because Frm_Logintoken only gets it's value when i click submit .
<input type="hidden" name="Frm_Logintoken" id="Frm_Logintoken" value="">
full page code
i found this online /getObj\("Frm_Logintoken"\).value = "(.*)";/g but when i run it ... it gives me the same line again ! it's full code
another regular expression i found but don't even know how to use it
Example of a regular expression to search:
before_egrep='N1:getObj("Frm_Logintoken").value = "(\w+)"'
Here, N1 is assigned the value of the back reference - the
expression in parentheses. \w + denotes the main compound characters,
this is a synonym for "[_[:alnum:]]". Once again - pay attention to
the brackets - this is the back link. At the same time, there are also
parentheses in the source code fragment - they need to be escaped
i am trying to make an auto login script that works in the background like it
doesn't show the user the login form page but the only the page after it
and i have found this code online too but don't know what's about
it contains xhr .
the line that Attracted my attention is
/getObj\("Frm_Logintoken"\).value = "(.*)";/g
when i run it ... it gives me the line again !
some notes :
i have tried document.getElementById("Frm_Logintoken").value but it gives me empty "" because
Frm_Logintoken only gets it's value when i click submit .
the page will not even accept the correct password if the Frm_Logintoken token value isn't the same as one in the page.
the Frm_Logintoken is a token generated by the page and it basically increment by one on each successful login.

I'm not so sure about suggestion of an expression for helping or ameliorating to help solving your problem, yet if we wish to extract certain attributes and values from the proposed input tag, we would be likely starting with an expression similar to:
name="(.+?)"|id="(.+?)"|value="(.+)?"
which uses alternation to simultaneously collect values of certain attributes, if so would be desired.
Demo
RegEx
If this expression wasn't desired and you wish to modify it, please visit this link at regex101.com.
RegEx Circuit
jex.im visualizes regular expressions:

To get your value you might use a capturing group ([^"]+) and a negated character class:
\bgetObj\("Frm_Logintoken"\)\.value = "([^"]+)";
Regex demo | Javascript demo
For example:
let str = `getObj("Frm_Logintoken").value = "3";`;
let pattern =/\bgetObj\("Frm_Logintoken"\)\.value = "([^"]+)";/;
console.log(str.match(pattern)[1]); //3

Regex with multiple start and end characters that must be the same

I would like to be able to search for strings inside a special tag in a string in JavaScript. Strings in JavaScript can start with either " or ' character.
Here an example to illustrate what I want to do. My custom tag is called <my-tag. My regex is /('|")*?<my-tag>((.|\n)[^"']*?)<\/my-tag>*?('|")/g. I use this regex pattern on the following strings:
var a = '<my-tag>Hello World</my-tag>'; //is found as expected
var b = "<my-tag>Hello World" + '</my-tag>'; //is NOT found, this is good!
var c = "<my-tag>Hello World</my-tag>"; //is found as expected
var d = '<my-tag>something "special"</my-tag>'; //here the " char causes a problem
var e = "<my-tag>something 'special'</my-tag>"; //here the " char causes a problem
It works well with a and also c where it finds the tag with the containing text. It also does not find the text in b which is what I want. But in case d and e the tag with content is not found due to the occurrence of the " and ' character. What I want is a regex where inside the tag " is allowed if the string is start with ', and vice versa.
Is it possible to achieve this with one regex, or is the only thing I can do is to work with two separate regex expressions like
/(")*?<my-tag>((.|\n)[^']*?)<\/my-tag>*?(")/g and /(')*?<my-tag>((.|\n)[^"]*?)<\/my-tag>*?(')/g ?

It's not pretty, but I think this would work:
/("<my-tag>((.|\n)[^"]*?)<\/my-tag>"|'<my-tag>((.|\n)[^']*?)<\/my-tag>')/g

You should be able to use de match from the first match ('|") and reuse it for the second match. Something like the following:
/('|")<my-tag>.*?<\/my-tag>\1/g
This should make sure to match the same character at the beginning and the end.
But you really shouldn't use regex for parsing HTML.

Using .replace() at a specific index

Is there a function that can replace a string within a string once at a specific index? Example:
var string1="my text is my text";
var string2="my";
string1.replaceAt(string2,"your",10);
and the resultant output would be "my text is your text", Or:
var string1="my text is my text";
var string2="my";
string1.replaceAt(string2,"your",0);
in which case the result would be "your text is my text".

function ReplaceAt(input, search, replace, start, end) {
return input.slice(0, start)
+ input.slice(start, end).replace(search, replace)
+ input.slice(end);
}
jsfiddle here
PS. modify the code to add empty checks, boundary checks etc.

From the "related questions" bar, this old answer seems to be applicable to your case. Replacing a single character (in my referenced question) is not very different from replacing a string.
How do I replace a character at a particular index in JavaScript?

Replace text (change case) in a textbox using Javascript

I am trying to build a sort of intelli-sense text input box, where as the user types, the 'and' is replaced by 'AND \n' (i.e. on each 'and', the 'and' is capitalized and user goes to new line).
The Javascript I used for this is:
function Validate()
{
document.getElementById("search").value = document.getElementById("search").value.replace("and","AND \n"); //new line for AND
}
The HTML part is like this:
< textarea type="text" name="q" id="search" spellcheck="false" onkeyup='Validate();'>< /textarea>
Though the above script works well on Firefox and Chrome, it sort-of misbehaves on Internet Explorer (brings the cursor to the end of the text on each 'KeyUp').
Also the above code doesn't work for the other variants of 'and' like 'And', 'anD' or even 'AND' itself.

I think the actual answer here is a mix of the two previous:
onkeyup="this.value = this.value.replace(/\band\b/ig, ' AND\n')"
You need the i to make the search case insensitive and the g to make sure you replace all occurrences. This is not very efficient, as it'll replace previous matches with itself, but it'll work.
To make it a separate function:
function validate() {
document.getElementById('search') = document.getElementById('search').replace(/\band\b/ig, ' AND\n');
}

If you alter the textarea contents while the user is typing the caret will always move to the end, even in Firefox and Chrome. Just try to edit something you already wrote and you'll understand me. You have to move the caret to the exact position where the users expects it, which also implies you have to detect text selections (it's a standard behaviour that typing when you have a selection removes the selected text).
You can find here some sample code. You might be able to use the doGetCaretPosition(), setCaretPosition() functions.

I tried to work around the problem and solved by using the following javascript:
function Validate() {
if( document.getElementById("search").value.search(/\band$(?!\n)/i) >= 0 ){ // for maintaining cursor position
document.getElementById("search").value = document.getElementById("search").value.replace(/\band$(?!\n)/i,"AND\n"); //new line for AND
}
}
Thin slicing the above problem and solution:
1) The function was being called on each key up, thus earlier "AND\n" was being repeated on each key up, thus inserting a blank line on each key press. I avoided the above by using the regex:
/\band$(?!\n)/i
\b = Like Word (to avoid SAND)
$ = End of line (as "and" will be replaced by "AND\n" thus it will always be end of line)
(?!\n) = Not followed by new line (to prevent repeatedly replacing "AND\n" on each key press)
i = To cover all variants of "and" including "And","anD" etc.
2) Internet Explorer was misbehaving and the cursor position was not maintained (moved to end) when the input was re-edited. This was caused (as hinted by Alvaro above) due to the replace function.
Thus I inserted an "if" statement to call replace function only when it is needed, i.e. only when there is some "and" needing replacement.
Thanks everyone for the help.

try using the following replace() statement:
replace(/\band(?!$)/ig, "And\n")
since this is being called repeatedly against the altered string you have to make sure that the "and" is not followed by a line break.
example (uses a loop and function to simulate the user typing the letters in):
function onkeyup() {
var str = this;
return this.replace(/\band(?!$)/ig, "And\n");
};
var expected = "this is some sample text And\n is separated by more text And\n stuff";
var text = "this is some sample text and is separated by more text and stuff";
var input = "";
var output = "";
for(var i = 0, len = text.length; i < len; i++ ) {
input += text.substr(i,1);
output = onkeyup.call(input);
}
var result = expected == output;
alert(result);
if( !result ) {
alert("expected: " + expected);
alert("actual: " + output);
}
you can test this out here: http://bit.ly/8kWLtr

You need to write a JS code that run in both IE and FireFox. I think this is what you need:
var s = document.getElementbyId('Search');
s.value = s.value.replace('and', 'AND \n');

I think you want your replace call to look like this:
replace(/\band\b/i,"AND \n") (see below)
That way it is not case sensitive (/i), and only takes single words that match and, so 'sand' and similar words that contain 'and' don't match, only 'and' on it's own.
EDIT: I played around with it based on the comments and I think this working example is what is wanted.
Replace the onKeyUp event with onBlur:
<textarea type="text" name="q" id="search" spellcheck="false" onblur='Validate();'></textarea></body>
So that the validate function is only run when the user leaves the text box. You could also run it onSubmit.
I also added a global switch (g) and optional trailing whitespace (\s?) to the regex:
replace(/\band\b\s?/ig,"AND \n")
This causes input like this:
sand and clay and water
to be transformed into this when you leave the text box:
sand AND
clay AND
water
You should probably test this against a bunch more cases.