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Regex for matching only first of two same characters in a string

I have these two strings: "1-2" and "1--2".
I would like to have a regex that would match only the first occurrence of the hyphen in both strings, such that the split would then be: [1,2] and [1,-2]. How would I achieve this, since I have been wracking my brain for too long on this now?
EDIT: The two strings can also occur in the same string such that: "1-2-1--2". Therefore a single regular expression covering both cases would be in order.

You can use this split with a word boundary before -:
let s='1-2-1--2'
let arr = s.split(/\b-/)
console.log(arr)
//=> [1, 2, 1, -2)

You can use simple split(), but with replacement. For example,
var str = '1-2-1--2';
var numArr = str.replace(/--/g, '-~') // The tilde (~) have no mean, this is a charceter for mark a negative number
.split('-')
.map(function(n) { return Number(n.replace('~', '-')); });
console.log(numArr);

I think you're looking for something like this:
(-?[0-9]+)-(-?[0-9]+)
where the first and the second group could have a negative sign
UPDATE:
based on your edit, this implementation would do the job:
var str = '-1--2-2--34-1';
var regex = /(-?\d+)-?/g;
var matches = [];
while((match = regex.exec(str))) {
matches.push(match[1]);
}
console.log(matches);
I prefer using split, but it's fine if you only want to use RegEx.

Convert string with index in brackets to JSON array

I have various strings with numbers in brackets like "[4]Motherboard, [25]RAM" how can I convert such a string to a JSON array (keeping both ids and values) like this:
{"data":[
{"id":"4","item":"Motherboard"},
{"id":"25","item":"RAM"}
]};
I'm tried using split(",") to create the array but I really can't find out how to get the inner data in this case.

You could use a regular expression, which takes the number and the string, and assign it as property to an object.
var string = "[4]Motherboard, [25]RAM",
data = string.split(', ').map(function (a) {
var p = a.match(/^\[(\d+)\](.+)$/);
return { id: p[1], item: p[2] };
});
console.log(data);

Here one way to do it. The pattern \[(\d+?)\](.+) works like this:
(…) is a capture group. Just means whatever matches within the brackets will be a token in the result.
\d means a digit
\d+ means a digit, one or more times
\d+? means a digit, one or more times, but as few as possibile before the pattern matches something else.
.+ means any character, one or more times.
[ and ] have a special meaning in regular expression, so if you actually want to match the characters themselves, you need to escape them like so \[ and \].
The double backslashes \\ are just a JS oddity when defining a regex via a string as opposed to using a /literal/. Just two ways of saying the same thing.
There's plenty of resources to learn regex syntax, and http://regex101.com is a great place to play with patterns and experiment.
var input = "[4]Motherboard, [25]RAM";
var pattern = '\\[(\\d+?)\\](.+)';
var result = input.split(',').map(function (item) {
var matches = item.match(new RegExp(pattern));
return {id: matches[1], val: matches[2]};
});
console.log(result)

function toArray(string) {
return {
data: string.split(",").map(function(str) {
str = str.trim();
return {
id: str.substring(1, str.indexOf("]")),
item: str.substring(str.indexOf("]") + 1),
};
}),
};
}

Regexp, capture between parentheses, javascript

I have regexp that extracts values between parentheses.
It's working most of the time but not when it ends with a parentheses
var val = 'STR("ABC(t)")';
var regExp = /\(([^)]+)\)/;.
var matches = regExp.exec(val);
​
console.log(matches[1]); //"ABC(t"
What I want is "ABC(t)".
Any ideas how I can modify my regexp to Achive this?
Update
The value is always inside the parentheses.
Some examples:
'ASD("123")'; => '123'
'ASD(123)'; => '123'
'ASD(aa(10)asda(459))'; => 'aa(10)asda(459)'
So first there is some text (always text). Then there is a (, and it always ends with a ). I want the value between.

You may use greedy dot matching inside Group 1 pattern: /\((.+)\)/. It will match the first (, then any 1+ chars other than linebreak symbols and then the last ) in the line.
var vals = ['STR("ABC(t)")', 'ASD("123")', 'ASD(123)', 'ASD(aa(10)asda(459))'];
var regExp = /\((.+)\)/;
for (var val of vals) {
var matches = regExp.exec(val);
console.log(val, "=>", matches[1]);
}
Answering the comment: If the texts to extract must be inside nested balanced parentheses, either a small parsing code, or XRegExp#matchRecursive can help. Since there are lots of parsing codes around on SO, I will provide XRegExp example:
var str = 'some text (num(10a ) ss) STR("ABC(t)")';
var res = XRegExp.matchRecursive(str, '\\(', '\\)', 'g');
console.log(res);
<script src="https://cdnjs.cloudflare.com/ajax/libs/xregexp/2.0.0/xregexp-all-min.js"></script>

Modify formatting-pattern to replace placeholders in string

I write currently a simple formatting function to replace some placeholders in a string.
var format = function (a, c) {
return a.replace(/{ *([^} ]+) *}/g, function (b, a) {
b = c;
a.replace(/[^.|\[\]]+/g, function (a) {
b = b[a];
});
return b;
});
};
The syntax uses currently curly-bracket notation {key}, I try now to modify the RegExp-pattern to work with one percent instead %key.
var pattern = /{ *([^} ]+) *}/g;
I tried to just replace the parentheses {} with a percent %, but this still doesn't work properly.
var pattern = /% *([^% ]+) */g;
The original pattern works with the following conditions as expected:
var data = {
obj: {
foo: 'Foo',
bar: 'Bar'
},
arr: ['Foo', 'Bar']
};
var objTest = '{obj.foo}, is not equal to {obj.bar}.'
format(objTest, data) // => 'Foo, is not equal to Bar.'
var arrTest = '{arr[0]}, is not equal to {arr[1]}.'
format(arrTest, data) // => 'Foo, is not equal to Bar.'
If we use my modified pattern it seems that the last character after each placeholder-replacement will be removed:
'%obj.foo, is not equal to %obj.bar.' // => 'undefined is not equal to Bar'
'%arr[0], is not equal to %arr[1]' // => 'undefined is not equal to Bar'
Any ideas how to modify the pattern to make it possible to use it with percentage % instead of curly-brackets {}?

You can use this pattern:
var regex = /%([^\b]+)/g;
which means a % sign followed by a complete word. This excludes whitespace characters, underscores, etc.
If you instead want to be able to use those characters as well, you can write:
var regex = /%(\S+)/g;
which is the equivalent of:
var regex = /%([^\s]+)/g;

The reason for this is that your modified regex pattern does not know when to stop matching. In the previous one it terminated at the following } symbol.
This is not an easy thing to fix as there is a myriad of possibilities that could be seen to end your format, here you have a piece of punctuation at the end of each replacement string, i.e. a full stop %arr[1]. or comma %obj.foo,.
So to make this work in your case toy could replace } in the original pattern with [\.,] i.e.
/% *([^% ]+) *[\.,]/g
This will work, but now your replacement pattern needs to always be terminated with either a full stop or comma which i suspect is not exactly what you want. Better to terminate with a know character such as % which would make your matching pattern /% *([^% ]+) *%/g and your format %obj.foo% and you can output a % by doubling up i.e. %obj.bar%%%

Javascript split function not correct worked with specific regex

I have a problem. I have a string - "\,str\,i,ing" and i need to split by comma before which not have slash. For my string - ["\,str\,i", "ing"]. I'm use next regex
myString.split("[^\],", 2)
but it's doesn't worked.

Well, this is ridiculous to avoid the lack of lookbehind but seems to get the correct result.
"\\,str\\,i,ing".split('').reverse().join('').split(/,(?=[^\\])/).map(function(a){
return a.split('').reverse().join('');
}).reverse();
//=> ["\,str\,i", "ing"]

Not sure about your expected output but you are specifying string not a regex, use:
var arr = "\,str\,i,ing".split(/[^\\],/, 2);
console.log(arr);
To split using regex, wrap your regex in /..../

This is not easily possible with js, because it does not support lookbehind. Even if you'd use a real regex, it would eat the last character:
> "xyz\\,xyz,xyz".split(/[^\\],/, 2)
["xyz\\,xy", "xyz"]
If you don't want the z to be eaten, I'd suggest:
var str = "....";
return str.split(",").reduce(function(res, part) {
var l = res.length;
if (l && res[l-1].substr(-1) == "\\" || l<2)
// ^ ^^ ^
// not the first was escaped limit
res[l-1] += ","+part;
else
res.push(part);
return;
}, []);

Reading between the lines, it looks like you want to split a string by , characters that are not preceded by \ characters.
It would be really great if JavaScript had a regular expression lookbehind (and negative lookbehind) pattern, but unfortunately it does not. What it does have is a lookahead ((?=) )and negative lookahead ((?!)) pattern. Make sure to review the documentation.
You can use these as a lookbehind if you reverse the string:
var str,
reverseStr,
arr,
reverseArr;
//don't forget to escape your backslashes
str = '\\,str\\,i,ing';
//reverse your string
reverseStr = str.split('').reverse().join('');
//split the array on `,`s that aren't followed by `\`
reverseArr = reverseStr.split(/,(?!\\)/);
//reverse the reversed array, and reverse each string in the array
arr = reverseArr.reverse().map(function (val) {
return val.split('').reverse().join('');
});

You picked a tough character to match- a forward slash preceding a comma is apt to disappear while you pass it around in a string, since '\,'==','...
var s= 'My dog, the one with two \\, blue \\,eyes, is asleep.';
var a= [], M, rx=/(\\?),/g;
while((M= rx.exec(s))!= null){
if(M[1]) continue;
a.push(s.substring(0, rx.lastIndex-1));
s= s.substring(rx.lastIndex);
rx.lastIndex= 0;
};
a.push(s);
/* returned value: (Array)
My dog
the one with two \, blue \,eyes
is asleep.
*/

Find something which will not be present in your original string, say "###". Replace "\\," with it. Split the resulting string by ",". Replace "###" back with "\\,".
Something like this:
<script type="text/javascript">
var s1 = "\\,str\\,i,ing";
var s2 = s1.replace(/\\,/g,"###");
console.log(s2);
var s3 = s2.split(",");
for (var i=0;i<s3.length;i++)
{
s3[i] = s3[i].replace(/###/g,"\\,");
}
console.log(s3);
</script>
See JSFiddle