Develop Reference

Regular expression in Javascript: table of positions instead of table of occurrences

Regular expressions are most powerful. However, the result they return is sometimes useless:
For example:
I want to manage a CSV string using semicolons.
I define a string like:
var data = "John;Paul;Pete;Stuart;George";
If I use the instruction:
var tab = data.match(/;/g)
after what, "tab" contains an array of 4 ";" :
tab[0]=";", tab[1]=";", tab[2]=";", tab[3]=";"
This array is not useful in the present case, because I knew it even before using the regular expression.
Indeed, what I want to do is 2 things:
1stly: Suppress the 4th element (not "Stuart" as "Stuart", but "Stuart" as 4th element)
2ndly: Replace the 3rd element by "Ringo" so as to get back (to where you once belonged!) the following result:
data == "John;Paul;Ringo;George";
In this case, I would greatly prefer to obtain an array giving the positions of semicolons:
tab[0]=4, tab[1]=9, tab[2]=14 tab[3]=21
instead of the useless (in this specific case)
tab[0]=";", tab[1]=";", tab[2]=";", tab[3]=";"
So, here's my question: Is there a way to obtain this numeric array using regular expressions?

To get tab[0]=4, tab[1]=9, tab[2]=14 tab[3]=21, you can do
var tab = [];
var startPos = 0;
var data = "John;Paul;Pete;Stuart;George";
while (true) {
var currentIndex = data.indexOf(";", startPos);
if (currentIndex == -1) {
break;
}
tab.push(currentIndex);
startPos = currentIndex;
}
But if the result wanted is "John;Paul;Ringo;George", you can do
var tab = data.split(';'); // Split the string into an array of strings
tab.splice(3, 1); // Suppress the 4th element
tab[2] = "Ringo"; // Replace the 3rd element by "Ringo"
var str = tab.join(';'); // Join the elements of the array into a string
The second approach is maybe better in your case.
String.split
Array.splice
Array.join

You should try a different approach, using split.
tab = data.split(';') will return an array of the form
tab[0]="John", tab[1]="Paul", tab[2]="Pete", tab[3]="Stuart", tab[4]="George"
You should be able to achieve your goal with this array.

Why use a regex to perform this operation? You have a built-in function split, which can split your string based on the delimiter you pass.
var data = "John;Paul;Pete;Stuart;George";
var temp=data.split(';');
temp[0],temp[1]...

How to remove the last matched regex pattern in javascript

I have a text which goes like this...
var string = '~a=123~b=234~c=345~b=456'
I need to extract the string such that it splits into
['~a=123~b=234~c=345','']
That is, I need to split the string with /b=.*/ pattern but it should match the last found pattern. How to achieve this using RegEx?
Note: The numbers present after the equal is randomly generated.
Edit:
The above one was just an example. I did not make the question clear I guess.
Generalized String being...
<word1>=<random_alphanumeric_word>~<word2>=<random_alphanumeric_word>..~..~..<word2>=<random_alphanumeric_word>
All have random length and all wordi are alphabets, the whole string length is not fixed. the only text known would be <word2>. Hence I needed RegEx for it and pattern being /<word2>=.*/

This doesn't sound like a job for regexen considering that you want to extract a specific piece. Instead, you can just use lastIndexOf to split the string in two:
var lio = str.lastIndexOf('b=');
var arr = [];
var arr[0] = str.substr(0, lio);
var arr[1] = str.substr(lio);
http://jsfiddle.net/NJn6j/

I don't think I'd personally use a regex for this type of problem, but you can extract the last option pair with a regex like this:
var str = '~a=123~b=234~c=345~b=456';
var matches = str.match(/^(.*)~([^=]+=[^=]+)$/);
// matches[1] = "~a=123~b=234~c=345"
// matches[2] = "b=456"
Demo: http://jsfiddle.net/jfriend00/SGMRC/

Assuming the format is (~, alphanumeric name, =, and numbers) repeated arbitrary number of times. The most important assumption here is that ~ appear once for each name-value pair, and it doesn't appear in the name.
You can remove the last token by a simple replacement:
str.replace(/(.*)~.*/, '$1')
This works by using the greedy property of * to force it to match the last ~ in the input.
This can also be achieved with lastIndexOf, since you only need to know the index of the last ~:
str.substring(0, (str.lastIndexOf('~') + 1 || str.length() + 1) - 1)
(Well, I don't know if the code above is good JS or not... I would rather write in a few lines. The above is just for showing one-liner solution).

A RegExp that will give a result that you may could use is:
string.match(/[a-z]*?=(.*?((?=~)|$))/gi);
// ["a=123", "b=234", "c=345", "b=456"]
But in your case the simplest solution is to split the string before extract the content:
var results = string.split('~'); // ["", "a=123", "b=234", "c=345", "b=456"]
Now will be easy to extract the key and result to add to an object:
var myObj = {};
results.forEach(function (item) {
if(item) {
var r = item.split('=');
if (!myObj[r[0]]) {
myObj[r[0]] = [r[1]];
} else {
myObj[r[0]].push(r[1]);
}
}
});
console.log(myObj);
Object:
a: ["123"]
b: ["234", "456"]
c: ["345"]

(?=.*(~b=[^~]*))\1
will get it done in one match, but if there are duplicate entries it will go to the first. Performance also isn't great and if you string.replace it will destroy all duplicates. It would pass your example, but against '~a=123~b=234~c=345~b=234' it would go to the first 'b=234'.
.*(~b=[^~]*)
will run a lot faster, but it requires another step because the match comes out in a group:
var re = /.*(~b=[^~]*)/.exec(string);
var result = re[1]; //~b=234
var array = string.split(re[1]);
This method will also have the with exact duplicates. Another option is:
var regex = /.*(~b=[^~]*)/g;
var re = regex.exec(string);
var result = re[1];
// if you want an array from either side of the string:
var array = [string.slice(0, regex.lastIndex - re[1].length - 1), string.slice(regex.lastIndex, string.length)];
This actually finds the exact location of the last match and removes it regex.lastIndex - re[1].length - 1 is my guess for the index to remove the ellipsis from the leading side, but I didn't test it so it might be off by 1.

Grab url parameter with jquery and put into input

I am trying to grab a specific paramater from a url such as www.internets.com?param=123456
I am trying it with something like this..
$j.extend({
getUrlVars: function(){
return window.location.href.slice(window.location.href.indexOf('?')).split(/[&?]{1}[\w\d]+=/);
}
});
var allVars = $j.getUrlVars('param');
The weird thing is the variable is returning a comma so in this example it looks like ,123456
Where is that coming from?!

split returns an array of substrings, so the comma is coming from the serialization of the array.

Have a look here: http://jquery-howto.blogspot.com/2009/09/get-url-parameters-values-with-jquery.html
This seems to work for me.

You're asking the javascript to split the string into an array based on the rules in your regex, so the string "?param=123456" turns into an array where everything up to the = is simply a separator, so it sees two keys: an empty string and 123456.
EDIT - You can still use split, just use a different separator. The indexOf is telling it to look at the substring after the position of the '?', so if you split on '=' it would provide an array where one value is a parameter name (possibly with a '?' or '&', so just remove it) and the next value is the value sent in after the equal sign.
You can also get a little more in depth with your regex and processing like so:
var q = window.location.search; // returns everything after '?'
var regEx = /[^?& =]([\w]*)[^!?& =]/g;
var array = q.match(regEx);
var vars = new Array();
for (var i = 0; i < array.length; i++) {
if ((i % 2) == 0) {
vars[array[i]] = array[i + 1];
}
}
Which will leave you with an array where the keys are the param names, and their values are the associated values from the query string.

how do I capture something after something else? like a referer=someString

I have ref=Apple
and my current regex is
var regex = /ref=(.+)/;
var ref = regex.exec(window.location.href);
alert(ref[0]);
but that includes the ref=
now, I also want to stop capturing characters if a & is at the end of the ref param. cause ref may not always be the last param in the url.

You'll want to split the url parameters, rather than using a regular expression.
Something like:
var get = window.location.href.split('?')[1];
var params = get.split('&');
for (p in params) {
var key = params[p].split('=')[0];
var value = params[p].split('=')[1];
if (key == 'ref') {
alert('ref is ' + value);
}
}

Use ref[1] instead.
This accesses what is captured by group 1 in your pattern.
Note that there's almost certainly a better way to do key/value parsing in Javascript than regex.
References
regular-expressions.info/Brackets for Capturing

You are using the ref wrong, you should use ref[1] for the (.+), ref[0] is the whole match.
If & is at the end, modify the regexp to /ref=([^&]+)/, to exclude &s.
Also, make sure you urldecode (unescape in JavaScript) the match.

Capture only word characters and numbers:
var regex = /ref=(\w+)/;
var ref = regex.exec(window.location.href);
alert(ref[1]);
Capture word characters, numbers, - and _:
var regex = /ref=([\w_\-]+)/;
var ref = regex.exec(window.location.href);
alert(ref[1]);
More information about Regular Expressions (the basics)

try this regex pattern ref=(.*?)&
This pattern will match anything after ref= and stop before '&'
To get the value of m just use following code:
var regex = /ref=(.*?)&/;
var ref = regex.exec(window.location.href);
alert(ref[1]);

How to extract a string using JavaScript Regex?

I'm trying to extract a substring from a file with JavaScript Regex. Here is a slice from the file :
DATE:20091201T220000
SUMMARY:Dad's birthday
the field I want to extract is "Summary". Here is the approach:
extractSummary : function(iCalContent) {
/*
input : iCal file content
return : Event summary
*/
var arr = iCalContent.match(/^SUMMARY\:(.)*$/g);
return(arr);
}

function extractSummary(iCalContent) {
var rx = /\nSUMMARY:(.*)\n/g;
var arr = rx.exec(iCalContent);
return arr[1];
}
You need these changes:
Put the * inside the parenthesis as
suggested above. Otherwise your matching
group will contain only one
character.
Get rid of the ^ and $. With the global option they match on start and end of the full string, rather than on start and end of lines. Match on explicit newlines instead.
I suppose you want the matching group (what's
inside the parenthesis) rather than
the full array? arr[0] is
the full match ("\nSUMMARY:...") and
the next indexes contain the group
matches.
String.match(regexp) is
supposed to return an array with the
matches. In my browser it doesn't (Safari on Mac returns only the full
match, not the groups), but
Regexp.exec(string) works.

You need to use the m flag:
multiline; treat beginning and end characters (^ and $) as working
over multiple lines (i.e., match the beginning or end of each line
(delimited by \n or \r), not only the very beginning or end of the
whole input string)
Also put the * in the right place:
"DATE:20091201T220000\r\nSUMMARY:Dad's birthday".match(/^SUMMARY\:(.*)$/gm);
//------------------------------------------------------------------^ ^
//-----------------------------------------------------------------------|

Your regular expression most likely wants to be
/\nSUMMARY:(.*)$/g
A helpful little trick I like to use is to default assign on match with an array.
var arr = iCalContent.match(/\nSUMMARY:(.*)$/g) || [""]; //could also use null for empty value
return arr[0];
This way you don't get annoying type errors when you go to use arr

This code works:
let str = "governance[string_i_want]";
let res = str.match(/[^governance\[](.*)[^\]]/g);
console.log(res);
res will equal "string_i_want". However, in this example res is still an array, so do not treat res like a string.
By grouping the characters I do not want, using [^string], and matching on what is between the brackets, the code extracts the string I want!
You can try it out here: https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_match_regexp
Good luck.

(.*) instead of (.)* would be a start. The latter will only capture the last character on the line.
Also, no need to escape the :.

You should use this :
var arr = iCalContent.match(/^SUMMARY\:(.)*$/g);
return(arr[0]);

this is how you can parse iCal files with javascript
function calParse(str) {
function parse() {
var obj = {};
while(str.length) {
var p = str.shift().split(":");
var k = p.shift(), p = p.join();
switch(k) {
case "BEGIN":
obj[p] = parse();
break;
case "END":
return obj;
default:
obj[k] = p;
}
}
return obj;
}
str = str.replace(/\n /g, " ").split("\n");
return parse().VCALENDAR;
}
example =
'BEGIN:VCALENDAR\n'+
'VERSION:2.0\n'+
'PRODID:-//hacksw/handcal//NONSGML v1.0//EN\n'+
'BEGIN:VEVENT\n'+
'DTSTART:19970714T170000Z\n'+
'DTEND:19970715T035959Z\n'+
'SUMMARY:Bastille Day Party\n'+
'END:VEVENT\n'+
'END:VCALENDAR\n'
cal = calParse(example);
alert(cal.VEVENT.SUMMARY);