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add hyphen after every fourth character in a string seperated by comma

I have a string as 1111111111,2222222222,333333333,....
I want to modify it as 1111-111111,2222-222222,3333-33333,....
the regex I am using is this..
var num = '1111111111,2222222222,333333333,....';
var newNum = num.toString().match(/.{4}/g).join('-');
this add hyphen after every fourth character but I am unable to reset when comma is found.

You can use the following regex:
\b\d{4}
with replacement $&-
demo
var num = '1111111111,2222222222,333333333,....';
console.log(num.replace(/\b\d{4}/g, "$&-"));

Try following
let str = '1111111111,2222222222,333333333';
let res = str.split(",").map(s => s.slice(0,4) + "-" + s.slice(4, s.length-1)).join(",");
console.log(res);

You can also use split() and substr() to get that:
var str = '1111111111,2222222222,333333333';
var res =[];
str.split(',').forEach((item)=>{
res.push(item.substr(0,4)+'-'+item.substr(4,item.length));
});
console.log(res);

JavaScript RegExp - find all prefixes up to a certain character

I have a string which is composed of terms separated by slashes ('/'), for example:
ab/c/def
I want to find all the prefixes of this string up to an occurrence of a slash or end of string, i.e. for the above example I expect to get:
ab
ab/c
ab/c/def
I've tried a regex like this: /^(.*)[\/$]/, but it returns a single match - ab/c/ with the parenthesized result ab/c, accordingly.
EDIT :
I know this can be done quite easily using split, I am looking specifically for a solution using RegExp.

NO, you can't do that with a pure regex.
Why? Because you need substrings starting at one and the same location in the string, while regex matches non-overlapping chunks of text and then advances its index to search for another match.
OK, what about capturing groups? They are only helpful if you know how many /-separated chunks you have in the input string. You could then use
var s = 'ab/c/def'; // There are exact 3 parts
console.log(/^(([^\/]+)\/[^\/]+)\/[^\/]+$/.exec(s));
// => [ "ab/c/def", "ab/c", "ab" ]
However, it is unlikely you know that many details about your input string.
You may use the following code rather than a regex:
var s = 'ab/c/def';
var chunks = s.split('/');
var res = [];
for(var i=0;i<chunks.length;i++) {
res.length > 0 ? res.push(chunks.slice(0,i).join('/')+'/'+chunks[i]) : res.push(chunks[i]);
}
console.log(res);
First, you can split the string with /. Then, iterate through the elements and build the res array.

I do not think a regular expression is what you are after. A simple split and loop over the array can give you the result.
var str = "ab/c/def";
var result = str.split("/").reduce(function(a,s,i){
var last = a[i-1] ? a[i-1] + "/" : "";
a.push(last + s);
return a;
}, []);
console.log(result);
or another way
var str = "ab/c/def",
result = [],
parts=str.split("/");
while(parts.length){
console.log(parts);
result.unshift(parts.join("/"));
parts.pop();
}
console.log(result);
Plenty of other ways to do it.

You can't do it with a RegEx in javascript but you can split parts and join them respectively together:
var array = "ab/c/def".split('/'), newArray = [], key = 0;
while (value = array[key++]) {
newArray.push(key == 1 ? value : newArray[newArray.length - 1] + "/" + value)
}
console.log(newArray);

May be like this
var str = "ab/c/def",
result = str.match(/.+?(?=\/|$)/g)
.map((e,i,a) => a[i-1] ? a[i] = a[i-1] + e : e);
console.log(result);

Couldn't you just split the string on the separator character?
var result = 'ab/c/def'.split(/\//g);

Split the date! (It's a string actually)

I want to split this kind of String :
"14:30 - 19:30" or "14:30-19:30"
inside a javascript array like ["14:30", "19:30"]
so I have my variable
var stringa = "14:30 - 19:30";
var stringes = [];
Should i do it with regular expressions? I think I need an help

You can just use str.split :
var stringa = "14:30 - 19:30";
var res = str.split("-");

If you know that the only '-' present will be the delimiter, you can start by splitting on that:
let parts = input.split('-');
If you need to get rid of whitespace surrounding that, you should trim each part:
parts = parts.map(function (it) { return it.trim(); });
To validate those parts, you can use a regex:
parts = parts.filter(function (it) { return /^\d\d:\d\d$/.test(it); });
Combined:
var input = "14:30 - 19:30";
var parts = input.split('-').map(function(it) {
return it.trim();
}).filter(function(it) {
return /^\d\d:\d\d$/.test(it);
});
document.getElementById('results').textContent = JSON.stringify(parts);
<pre id="results"></pre>

Try this :
var stringa = "14:30 - 19:30";
var stringes = stringa.split("-"); // string is "14:30-19:30" this style
or
var stringes = stringa.split(" - "); // if string is "14:30 - 19:30"; style so it includes the spaces also around '-' character.
The split function breaks the strings in sub-strings based on the location of the substring you enter inside it "-"
. the first one splits it based on location of "-" and second one includes the spaces also " - ".
*also it looks more like 24 hour clock time format than data as you mentioned in your question.

var stringa = '14:30 - 19:30';
var stringes = stringa.split("-");

.split is probably the best way to go, though you will want to prep the string first. I would go with str.replace(/\s*-\s*/g, '-').split('-'). to demonstrate:
var str = "14:30 - 19:30"
var str2 = "14:30-19:30"
console.log(str.replace(/\s*-\s*/g, '-').split('-')) //outputs ["14:30", "19:30"]
console.log(str2 .replace(/\s*-\s*/g, '-').split('-')) //outputs ["14:30", "19:30"]

Don't forget that you can pass a RegExp into str.split
'14:30 - 19:30'.split(/\s*-\s*/); // ["14:30", "19:30"]
'14:30-19:30'.split(/\s*-\s*/); // ["14:30", "19:30"]

Replace strings from left until the first occuring string in Javascript

I am trying to figure out how to replace example:
sw1_code1_number1_jpg --> code1_number1_jpg
hon2_noncode_number2_jpg --> noncode_number2_jpg
ccc3_etccode_number3_jpg --> etccode_number3_jpg
ddd4_varcode_number4_jpg --> varcode_number4_jpg
So the results are all string after the first _
If it doesn't find any _ then do nothing.
I know how to find and replace strings, str.replace, indexof, lastindexof but dont know how remove up to the first found occurrence.
Thank You

Use the replace method with a regular expression:
"sw1_code1_number1_jpg".replace(/^.*?_/, "");

You could split your string and get a slice
var str = 'sw1_code1_number1_jpg';
var finalStr = str.split('_').slice(1).join('_') || str;
If your original string does not contain an underscore, then it returns the original string.
UPDATE A simpler one with slice (still works with strings not containing underscores)
var str = 'sw1_code1_number1_jpg';
var finalStr = str.slice(str.indexOf('_') + 1);
This one works in all cases because when no underscore is found, -1 is returned and as we add 1 to the index we call str.slice(0) which is equal to str.

There are several approaches you can take:
var str = 'sw1_code1_number1_jpg';
var arr = str.split('_');
arr.shift();
var newSfr = arr.join('_');
Or you could use slice or replace:
var str = 'sw1_code1_number1_jpg';
var newStr = str.slice(str.indexOf('_')+1);
Or
var newStr = 'sw1_code1_number1_jpg'.replace(/^[^_]+_/,'');

Regex remove repeated characters from a string by javascript

I have found a way to remove repeated characters from a string using regular expressions.
function RemoveDuplicates() {
var str = "aaabbbccc";
var filtered = str.replace(/[^\w\s]|(.)\1/gi, "");
alert(filtered);
}
Output: abc
this is working fine.
But if str = "aaabbbccccabbbbcccccc" then output is abcabc.
Is there any way to get only unique characters or remove all duplicates one?
Please let me know if there is any way.

A lookahead like "this, followed by something and this":
var str = "aaabbbccccabbbbcccccc";
console.log(str.replace(/(.)(?=.*\1)/g, "")); // "abc"
Note that this preserves the last occurrence of each character:
var str = "aabbccxccbbaa";
console.log(str.replace(/(.)(?=.*\1)/g, "")); // "xcba"
Without regexes, preserving order:
var str = "aabbccxccbbaa";
console.log(str.split("").filter(function(x, n, s) {
return s.indexOf(x) == n
}).join("")); // "abcx"

This is an old question, but in ES6 we can use Sets. The code looks like this:
var test = 'aaabbbcccaabbbcccaaaaaaaasa';
var result = Array.from(new Set(test)).join('');
console.log(result);