Develop Reference

regex to find specific strings in javascript

disclaimer - absolutely new to regexes....
I have a string like this:
subject=something||x-access-token=something
For this I need to extract two values. Subject and x-access-token.
As a starting point, I wanted to collect two strings: subject= and x-access-token=. For this here is what I did:
/[a-z,-]+=/g.exec(mystring)
It returns only one element subject=. I expected both of them. Where i am doing wrong?

The g modifier does not affect exec, because exec only returns the first match by specification. What you want is the match method:
mystring.match(/[a-z,-]+=/g)

No regex necessary. Write a tiny parser, it's easy.
function parseValues(str) {
var result = {};
str.split("||").forEach(function (item) {
var parts = item.split("=");
result[ parts[0] /* key */ ] = parts[1]; /* value */
});
return result;
}
usage
var obj = parseValues("subject=something||x-access-token=something-else");
// -> {subject: "something", x-access-token: "something-else"}
var subj = obj.subject;
// -> "something"
var token = obj["x-access-token"];
// -> "something-else"
Additional complications my arise when there is an escaping schema involved that allows you to have || inside a value, or when a value can contain an =.
You will hit these complications with regex approach as well, but with a parser-based approach they will be much easier to solve.

You have to execute exec twice to get 2 extracted strings.
According to MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec
If your regular expression uses the "g" flag, you can use the exec() method multiple times to find successive matches in the same string.
Usually, people extract all strings matching the pattern one by one with a while loop. Please execute following code in browser console to see how it works.
var regex = /[a-z,-]+=/g;
var string = "subject=something||x-access-token=something";
while(matched = regex.exec(string)) console.log(matched);

You can convert the string into a valid JSON string, then parse it to retrieve an object containing the expected data.
var str = 'subject=something||x-access-token=something';
var obj = JSON.parse('{"' + str.replace(/=/g, '":"').replace(/\|\|/g, '","') + '"}');
console.log(obj);

I don't think you need regexp here, just use the javascript builtin function "split".
var s = "subject=something1||x-access-token=something2";
var r = s.split('||'); // r now is an array: ["subject=something1", "x-access-token=something2"]
var i;
for(i=0; i<r.length; i++){
// for each array's item, split again
r[i] = r[i].split('=');
}
At the end you have a matrix like the following:
y x 0 1
0 subject something1
1 x-access-token something2
And you can access the elements using x and y:
"subject" == r[0][0]
"x-access-token" == r[1][0]
"something2" == r[1][1]

If you really want to do it with a pure regexp:
var input = 'subject=something1||x-access-token=something2'
var m = /subject=(.*)\|\|x-access-token=(.*)/.exec(input)
var subject = m[1]
var xAccessToken = m[2]
console.log(subject);
console.log(xAccessToken);
However, it would probably be cleaner to split it instead:
console.log('subject=something||x-access-token=something'
.split(/\|\|/)
.map(function(a) {
a = a.split(/=/);
return { key: a[0], val: a[1] }
}));

JavaScript regexp parsing an array of URLs

String
url(image1.png), url('image2.png'), url("image3.png")
Note the ' and " delimiters. It would be nice to handle them as well, but I'm happy if the first form is captured.
Result
var results = 'image1.png', 'image2.png', 'image3.png';
How?
I would like to use regular expressions in javascript to parse a string that is used as the CSS property of an element with multiple backgrounds. The aim is to get the url of the images that are put in the background of the element using CSS.
See more: http://www.css3.info/preview/multiple-backgrounds/
JSFiddle
http://jsfiddle.net/fcx9x59r/1/

For this particular string [^'"()]+(?=['")]) seems to work fine:
css = "url(image1.png), url('image2.png'), url(\"image3.png\")";
m = css.match(/[^'"()]+(?=['")])/g)
document.write(m)
In the general case, you have to resort to a loop, because JS doesn't provide a way to return all matching groups from a single call:
css = "url(image1.png), something else, url('image2.png'), url(\"image3.png\")";
urls = []
css.replace(/url\(['"]*([^'")]+)/g, function(_, $1) { urls.push($1) });
document.write(urls)

/url\(([^"']+?)\)|'([^'"]+?)'\)|"([^'"]+?)"\)/g
Try this.Grab the captures.See demo.
http://regex101.com/r/qQ3kG7/1

You could try the below code also.
> var s = 'url(image1.png), url(\'image2.png\'), url("image3.png")';
undefined
> var re = /url\((["'])?((?:(?!\1).|[^'"])*?)\1\)/g;
undefined
> var matches = [];
undefined
> var m;
undefined
> while ((m = re.exec(s)) != null) {
......... matches.push(m[2]);
......... }
3
> console.log(matches)
[ 'image1.png', 'image2.png', 'image3.png' ]
DEMO

Try this:
var results = str.match(/url\(['"]?[^\s'")]+['"]?\)/g)
.map(function(s) {
return s.match(/url\(['"]?([^\s'")]+)['"]?\)/)[1];
});
Demo

javascript get string before a character

I have a string that and I am trying to extract the characters before the quote.
Example is extract the 14 from 14' - €14.99
I am using the follwing code to acheive this.
$menuItem.text().match(/[^']*/)[0]
My problem is that if the string is something like €0.88 I wish to get an empty string returned. However I get back the full string of €0.88.
What I am I doing wrong with the match?

This is the what you should use to split:
string.slice(0, string.indexOf("'"));
And then to handle your non existant value edge case:
function split(str) {
var i = str.indexOf("'");
if(i > 0)
return str.slice(0, i);
else
return "";
}
Demo on JsFiddle

Nobody seems to have presented what seems to me as the safest and most obvious option that covers each of the cases the OP asked about so I thought I'd offer this:
function getCharsBefore(str, chr) {
var index = str.indexOf(chr);
if (index != -1) {
return(str.substring(0, index));
}
return("");
}

try this
str.substring(0,str.indexOf("'"));

Here is an underscore mixin in coffescript
_.mixin
substrBefore : ->
[char, str] = arguments
return "" unless char?
fn = (s)-> s.substr(0,s.indexOf(char)+1)
return fn(str) if str?
fn
or if you prefer raw javascript : http://jsfiddle.net/snrobot/XsuQd/
You can use this to build a partial like:
var beforeQuote = _.substrBefore("'");
var hasQuote = beforeQuote("14' - €0.88"); // hasQuote = "14'"
var noQoute = beforeQuote("14 €0.88"); // noQuote = ""
Or just call it directly with your string
var beforeQuote = _.substrBefore("'", "14' - €0.88"); // beforeQuote = "14'"
I purposely chose to leave the search character in the results to match its complement mixin substrAfter (here is a demo: http://jsfiddle.net/snrobot/SEAZr/ ). The later mixin was written as a utility to parse url queries. In some cases I am just using location.search which returns a string with the leading ?.

I use "split":
let string = "one-two-three";
let um = string.split('-')[0];
let dois = string.split('-')[1];
let tres = string.split('-')[2];
document.write(tres) //three

Use JavaScript string operations to cut out exact text

I'm trying to cut out some text from a scraped site and not sure what functions or library's I can use to make this easier:
example of code I run from PhantomJS:
var latest_release = page.evaluate(function () {
// everything inside this function is executed inside our
// headless browser, not PhantomJS.
var links = $('[class="interesting"]');
var releases = {};
for (var i=0; i<links.length; i++) {
releases[links[i].innerHTML] = links[i].getAttribute("href");
}
// its important to take note that page.evaluate needs
// to return simple object, meaning DOM elements won't work.
return JSON.stringify(releases);
});
Class interesting has what I need, surrounded by new lines and tabs and whatnot.
here it is:
{"\n\t\t\t\n\t\t\t\tI_Am_Interesting\n\t\t\t\n\t\t":null,"\n\t\t\t\n\t\t\t\tI_Am_Interesting\n\t\t\t\n\t\t":null,"\n\t\t\t\n\t\t\t\tI_Am_Interesting\n\t\t\t\n\t\t":null}
I tried string.slice("\n"); and nothing happened, I really want a effective way to be able to cut out strings like this, based on its relationship to those \n''s and \t's
By the way this was my split code:
var x = latest_release.split('\n');
Cheers.

Its a simple case of stripping out all whitespace. A job that regexes do beautifully.
var s = " \n\t\t\t\n\t\t\t\tI Am Interesting\n\t\t \t \n\t\t";
s = s.replace(/[\r\t\n]+/g, ''); // remove all non space whitespace
s = s.replace(/^\s+/, ''); // remove all space from the front
s = s.replace(/\s+$/, ''); // remove all space at the end :)
console.log(s);
Further reading: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/RegExp

var interesting = {
"\n\t\t\t\n\t\t\t\tI_Am_Interesting1\n\t\t\t\n\t\t":null,
"\n\t\t\t\n\t\t\t\tI_Am_Interesting2\n\t\t\t\n\t\t":null,
"\n\t\t\t\n\t\t\t\tI_Am_Interesting3\n\t\t\t\n\t\t":null
}
found = new Array();
for(x in interesting) {
found[found.length] = x.match(/\w+/g);
}
alert(found);

Could you try with "\\n" as pattern? your \n may be understood as plain string rather than special character

new_string = string.replace("\n", "").replace("\t", "");

Any javascript string function?

Some outside code is giving me a string value like..
null,402,2912,2909,2910,2913,2911,2914,2915,2388,2389,2390,
now i have to save this value to the data base but putting 0 in place of null in javascript. Is there any javascript string releated function to do this conversion?

You can simply use the replace function over and over again until all instances are replaced, but make sure that all your string will ever contain is the character sequence null or a number (and obviously the delimiting comma):
var str = "null,402,2912,null"
var index = str.indexOf("null");
while(index != -1) {
str = str.replace("null", "0");
index = str.indexOf("null");
}
You need to run a for loop because the function String.replace(search, rplc) will replace only the first instance of search with rplc. So we use the indexOf method to check, in each iteration, if the required term exists or not. Another alternative (and in my opinion, a better alternative would be:
var str = "null,402,2912,null"
var parts = str.split(",");
var data = []
for(var i=0; i<parts.length; i++) {
data[data.length] = parts[i]=="null"?0:parseInt(parts[i]);
}
Basically, what we are doing is that since you will anyways be converting this to an array of numbers (I presume, and sort of hope), we first split it into individual elements and then inspect each element to see if it is null and make the conversion accordingly.

This should answer your needs:
var str = 'null,402,2912,2909,2910,2913,2911,2914,2915,2388,2389,2390';
str.split(",").map(function (n) { var num = Number(n); return isNaN(num) ? 0 : num; });

The simplest solution is:
var inputString = new String("null,402,2912,2909,2910,2913,2911,2914,2915,2388,2389,2390,");
var outputString = inputString.replace("null", "0");

What I understood from your question is:
You want to replace null with 0 in a string.
You may use
string = "null,402,2912,2909,2910,2913,2911,2914,2915,2388,2389,2390,"
string.replace(/null/g,0)
Hope it helps.