Develop Reference

Find string position from a string

How do I find a string start and end position from a string. Is there a way to search the "m" and "g" coordinats or char position? given that there maybe multiple values. so far only upto start.
Find: myname.jpg
<img src="myname.jpg" id="men">
var start = x.indexOf("myname.jpg");
//10

You can use a combination of .indexOf() and .substr().
When there is a possibility of multiple matches, providing more context characters to .indexOf() can resolve the issue or you can use .lastIndexOf() to start the search from the end of the string. You can also pass regular expressions to many of the string related methods and that is probably the best solution for extracting the correct positions based on some search criteria.
var x = "thewholestring";
// Get position where "whole" starts
var start = x.indexOf("whole");
// Extract 5 characters starting at that position
var result = x.substr(start, 5);
console.log(result);

Javascript selecting to save one index of split()

I have a value - toggle-save_2
I want to extract the 2 part. The part after the underscore will always be what i need but the length of the former part, which in this case is toggle-save_, may vary (eg. notoggle-val_45). Though this length may vary it will always be separated from the end number by an underscore.
Right now I am using this
var current = this.id.split('_');
current = current[1];
to select the number.
What would be cool is if I could pass a variable to the split to only give me the second index of the result from the split.

Just select the 2nd index when you do the split.
var current = this.id.split('_')[1];

The best solution here would be to use lastIndexOf and substring, like this
function getLastPart(strObject) {
return strObject.substring(strObject.lastIndexOf("_") + 1);
}
console.log(getLastPart("toggle-save_2"));
// 2
console.log(getLastPart("notoggle-save_45"));
// 45
It is better for this case because, you already know that the _ will be somewhere near the last position. Since lastIndexOf starts from the last position, it would find _ very soon and all we need to do is to get the rest of the string from the next position.

There are often times I am breaking up a string where I only need the very last value of the result of String.prototype.split and consider the rest to be garbage no matter how many values the split produced.
When those cases arise, I like to chain Array.prototype.pop off of the split
var s = 'toggle-save_2',
current = s.split('_').pop();

The split method can only be limited from the end, and it will always return an array.
You don't need to use split, you can use string operations to get part of the string:
var current = this.id.substr(this.id.indexOf('_') + 1);

Matching and returning a regex between two values

I am trying to get the values from a string using regex, the value is that of the text between tt=" and "&
So, for example, "tt="Value"&" I would only want to get the word "Value" out of this.
So far I have this: /tt=.*&/ which gives me "tt=Value"&, Then, to get the value I am thinking to split the match on = and remove the 2 characters from the end. I feel though, that this would be an awful way to do this and would like to see if it could be done in the regex?

You're on the right track for matching the entire context inside of the string, but you want to use a capturing group to match/capture the value between the quotes instead of splitting on = and having to remove the two quote chars.
var r = 'tt="Value"&'.match(/tt="([^"]*)"/)[1];
if (r)
console.log(r); //=> "Value"

I know this isn't really the answer you are looking for since it doesn't involve regex but it's the way I usually do it.
strvariable = strvariable.Remove(0,strvariable.IndexOf("=") + 2);
strvariable = strvariable.Remove(strvariable.IndexOf("\""), strvariable.Length - strvariable.IndexOf("\""));
this would give you the result you were looking for which is Value in this instance.

javascript regex to extract the first character after the last specified character

I am trying to extract the first character after the last underscore in a string with an unknown number of '_' in the string but in my case there will always be one, because I added it in another step of the process.
What I tried is this. I also tried the regex by itself to extract from the name, but my result was empty.
var s = "XXXX-XXXX_XX_DigitalF.pdf"
var string = match(/[^_]*$/)[1]
string.charAt(0)
So the final desired result is 'D'. If the RegEx can only get me what is behind the last '_' that is fine because I know I can use the charAt like currently shown. However, if the regex can do the whole thing, even better.

If you know there will always be at least one underscore you can do this:
var s = "XXXX-XXXX_XX_DigitalF.pdf"
var firstCharAfterUnderscore = s.charAt(s.lastIndexOf("_") + 1);
// OR, with regex
var firstCharAfterUnderscore = s.match(/_([^_])[^_]*$/)[1]
With the regex, you can extract just the one letter by using parentheses to capture that part of the match. But I think the .lastIndexOf() version is easier to read.
Either way if there's a possibility of no underscores in the input you'd need to add some additional logic.

Using javascript regexp to find the first AND longest match

I have a RegExp like the following simplified example:
var exp = /he|hell/;
When I run it on a string it will give me the first match, fx:
var str = "hello world";
var match = exp.exec(str);
// match contains ["he"];
I want the first and longest possible match,
and by that i mean sorted by index, then length.
Since the expression is combined from an array of RegExp's, I am looking for a way to find the longest match without having to rewrite the regular expression.
Is that even possible?
If it isn't, I am looking for a way to easily analyze the expression, and arrange it in the proper order. But I can't figure out how since the expressions could be a lot more complex, fx:
var exp = /h..|hel*/

How about /hell|he/ ?

All regex implementations I know of will (try to) match characters/patterns from left to right and terminate whenever they find an over-all match.
In other words: if you want to make sure you get the longest possible match, you'll need to try all your patterns (separately), store all matches and then get the longest match from all possible matches.

You can do it. It's explained here:
http://www.regular-expressions.info/alternation.html
(In summary, change the operand order or group with question mark the second part of the search.)

You cannot do "longest match" (or anything involving counting, minus look-aheads) with regular expressions.
Your best bet is to find all matches, and simply compare the lengths in the program.

I don't know if this is what you're looking for (Considering this question is almost 8 years old...), but here's my grain of salt:
(Switching the he for hell will perform the search based on the biggest first)
var exp = /hell|he/;
var str = "hello world";
var match = exp.exec(str);
if(match)
{
match.sort(function(a, b){return b.length - a.length;});
console.log(match[0]);
}
Where match[0] is going to be the longest of all the strings matched.