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Regex remove all string start with special character

I have a string look like:
var str = https://sharengay.com/movie13.m3u8?pid=144.21.112.0&tcp=none
I want to remove at start ?pid= to end. The result look like:
var str = https://sharengay.com/movie13.m3u8
I tried to:
str = str.replace(/^(?:?pid=)+/g, "");
But it show error like:
Invalid regular expression: /^(?:?pid=)+/: Nothing to repeat

If you really want to do this at the string level with regex, it's simply replacing /\?pid=.*$/ with "":
str = str.replace(/\?pid=.*$/, "");
That matches ?pid= and everything that follows it (.*) through the end of the string ($).
Live Example:
var str = "https://sharengay.com/movie13.m3u8?pid=144.21.112.0&tcp=none";
str = str.replace(/\?pid=.*$/, "");
console.log(str);

You can use split
var str = "https://sharengay.com/movie13.m3u8?pid=144.21.112.0&tcp=none"
var result = str.split("?pid=")[0];
console.log(result);

You can simply use split(), which i think is simple and easy.
var str = "https://sharengay.com/movie13.m3u8?pid=144.21.112.0&tcp=none";
str = str.split("?pid");
console.log(str[0]);

You may create a URL object and concatenate the origin and the pathname:
var str = "https://sharengay.com/movie13.m3u8?pid=144.21.112.0&tcp=none";
var url = new URL(str);
console.log(url.origin + url.pathname);

You have to escape the ? and if you want to remove everything from that point you also need a .+:
str = str.replace(/\?pid=.+$/, "")

You can use split function to get only url without query string.
Here is the example.
var str = 'https://sharengay.com/movie13.m3u8?pid=144.21.112.0&tcp=none';
var data = str.split("?");
alert(data[0]);

how to replace first and last quotes with two different chars in this string "{0}"

I have a string "{0}". I want to replace first quotes with <Q> and second quote with </Q> in javascript.
Can anyone help me with a regex to do this.

I don't have any idea about regex but i thought it seems like this:
var str = "{0}";
var mapObj = {
'{':"<Q>{",
'}':"}</Q>"
};
var re = new RegExp(Object.keys(mapObj).join("|"),"gi");
str = str.replace(re, function(matched){
return mapObj[matched.toLowerCase()];
});
alert(str);
Please correct me, if i'm wrong.

2 strings replace javascript

I am a beginner, how do I combine them:
var mystring = "my.email#computer.com";
document.write(mystring.replace(/#/, "&&"));
prints my.email&&computer.com
var mystring = "my.email#computer.com";
document.write(mystring.replace(/\./, "##"));
prints my##email#computer.com
I have two questions:
How do I make this regex (mystring.replace(/./, "##") to after # change the dot to ## and how can I combine those two lines into one, and final read is:my.email&&computer##com

input : my.first.last.email#example.computer.com
result : my.first.last.email&&example##computer##com
Solution 1:
var mystring = "my.first.last.email#example.computer.com";
//replace '.' after '#' with '##', then replace '#' with '&&'.
var result = mystring.replace(/(?!.*#)\./g, "##").replace(/#/, "&&");
document.write(result);
Solution 2 (configurable):
var mystring = "my.email#computer.com";
var replacements = {
'#' : '&&',
'.' : '##'
};
var str = "my.first.last.email#example.computer.com";
//match latter part of the string
var result = str.replace(/#\w+(\.\w+)+/g, function(at_and_after) {
//replace all '.' and '#' in that part.
return at_and_after.replace(/#|\./g, function(m) { return replacements[m]});
});
document.write(result); //console.log(result) or alert(result) is a better way for demo

Try this...
var mystring = "my.email#computer.com";
document.write(mystring.replace(/(.*#.*)\./, "$1##").replace(/#/, "&&"));

You could use split to split the string at /#/ and apply the second regexp to the second part of the string, then join the results back together with &&.

This should work:
var mystring = "my.email#computer.com";
document.write(mystring.replace(/(.*?)(#)(.*?)(\.)(.*)/, "$1&&$3##$5"));
Result:
my.email&&computer##com
See it here working: http://jsfiddle.net/gnB85/

Try this:
var mystring = "my.email#computer.com"
document.write(mystring.replace(/\.(?!\w+#)/, '##').replace(/#/, '&&'));

Replace a string of the last 7 chars?

This is my code :
​var myStr = "/private_images/last-edit/image-work-med.png";​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​
and I'd like to replace the last 7 chars (med.png) with big.png. Or, as you can see, the last occurence after a - split.
How can I do it? I think about regex, but I'm not a champion with them. Tried :
myStr = myStr .replace(/-([^-]*)$/, "big" + '$1');
but it replace the last -, not the last occurence. So the result is /private_images/last-edit/image-workbigmed.png

I'll make a confession: I'm not so great with regexes either.
How about splitting up using split? Less concise, but easier to understand.
var myStr = "/private_images/last-edit/image-work-med.png";​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​
var strs = myStr.split('-');
// Change the last element.
strs[strs.length - 1] = "big.png";
// And put back the right string.
myStr = strs.join('-');

You could use a regex, or you could use a few string methods and make your intentions clear.
var idx = myStr.lastIndexOf("-");
var newStr = myStr.substring(0, idx) + "big.png";

Without using RegExp you could use:
var str = "/private_images/last-edit/image-work-med.png"
,replace = 'big.png'
,nwstr = str.slice(0,str.lastIndexOf('-')+1)+replace;
//=> nwstr now "/private_images/last-edit/image-work-big.png"
More 'functional':
var nwstr = function(s){
return s.replace(s.substr(-7),'');}(
'/private_images/last-edit/image-work-med.png'
)+'big.png'

var url = "/private_images/last-edit/image-work-med.png";
var index = url.lastIndexOf('-');
url = url.substring(0, index+1);
var url2 = "big.png";
var output = url.concat(url2); alert(output);
Check this

Just add '-' to your regex and to the replacement string:
myStr = myStr .replace(/-([^-]*)\.png$/, "-big.png");
Or if you want the file extension to be variable:
myStr = myStr .replace(/-([^-]*)\.([a-z]+)$/, "-big.$2");

Why not just use replace:
var myStr = "/private_images/last-edit/image-work-med.png";​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​
var newStr = myStr.replace("med.png", "big.png");
According to the requirements specified in your question this would suffice.

If you know it will be a .png file:
var ex = new Regex(#"-\w*.png$");
var myStr = "/private_images/last-edit/image-work-med.png";​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​
myStr = ex.Replace(myStr, "-big.png");
It works but if its a jpg it wont...

If you want to use string functions -
var myStr = "/private_images/last-edit/image-work-med.png";
var cleanedupStr = myStr.slice(0, myStr.lastIndexOf("-"));
String.slice

Regular Expression in JS

How do you trim all of the text after a comma using JS?
I have: string = Doyletown, PA
I want: string = Doyletown

var str = 'Doyletown, PA';
var newstr=str.substring(0,str.indexOf(',')) || str;
I added the || str to handle a scenario where the string has no comma

How about a split:
var string = 'Doyletown, PA';
var parts = string.split(',');
if (parts.length > 0) {
var result = parts[0];
alert(result); // alerts Doyletown
}

using regular expression it will be like:
var str = "Doyletown, PA"
var matches = str.match(/^([^,]+)/);
alert(matches[1]);
jsFiddle
btw: I would also prefer .split() method

Or more generally (getting all the words in a comma separated list):
//Gets all the words/sentences in a comma separated list and trims these words/sentences to get rid of outer spaces and other whitespace.
var matches = str.match(/[^,\s]+[^,]*[^,\s]+/g);

Try this:
str = str.replace(/,.*/, '');
Or play with this jsfiddle