How to Split my String in Javascript for special case

This would be a lot smoother with a mapcat operator in JS.

let input = 'a,"d,e,f",g'
var result = []
input.split('"').forEach((e, i) => {
    result = result.concat( i % 2 == 0 ? e.split(',') : e )
})
result = result.filter(e => e != "")

As ChristianFigueroa pointed out: This won't work for cases where the quotes don't surround the whole field: value,val"ue", "value"

However if that is not important for you: jsperf/speedtest

Strongly advise to parse CSV with a tested CSV-parser library instead of any regex.

CSV-parsers for JavaScript

Among the common ones example:

• Papa Parse
• JQuery-CSV
• D3.js DSV module, including a CSV parser

Example usages

Your example using

• .. Papa Parse, can auto-detect the delimiter and has already a default for quoted-strings: quoteChar: '"' (like yours). Try it online:

var csvInput = 'a,"d,e,f",g';
var results = Papa.parse(csvString);
console.log(results);

Output (copied from console):

{
  data: [
    "a",
    "d,e,f",
    "g"
  ],
  errors: []
  meta: {delimiter: ",", linebreak: "↵", aborted: false, truncated: false, cursor: 11}
}

• .. JQuery-CSV, you can try it online:

var input = 'a,"d,e,f",g';
var result = $.csv.toArray(input);
console.log(result);

// even configurable
$.csv.toArrays(input, {
  delimiter: "\"", // already the default, custom value delimiter character
  separator: ',', // already the default, custom field separator character
});

Output:

[
  "a",
  "d,e,f",
  "g"
]

Disadvantage of regular-expressions for CSV parsing

The regex for CSV-parsing can be either simple like split(',') or long, cumbersome and fragile - catasrophic backracking like described on regular-expressions.info: "A Real Example: Matching CSV Records".

Furthermore:

• a regex is not easy to configure.
• a regex is hard to document, maintain, modularize or extend.

If you still want to try, read

• Ben Nadel (2009): "Ask Ben: Parsing CSV Strings With Javascript Exec() Regular Expression Command"

Related questions

• Example JavaScript code to parse CSV data
• How can I parse a CSV string with JavaScript, which contains comma in data?
• Regex to to parse csv with nested quotes
• How to read data From *.CSV file using javascript?

you need to use regexp

var str = 'a,"d,e,f",g';
console.log(str.split(/,"|",/));

myarray = []
while (str) {
    start = str;
    str = str.replace(/(".*?"|[^",]+|)($|,)/, function(match, group1) {
        myarray.push(group1);
        return "";
    });
    if (str == start) break;
}

The code above goes through the CSV string, adding each value it can to the array myarray. If the value has a " as it's first character (may contain commas), it will match until it reaches the next closing ". Otherwise, the regex will just look for the next comma. If it finds something like a value without a closing ", it will automatically stop and myarray will include all the values up to that point that it failed. Empty values (two adjacent commas) will also work.

You can clean up the CSV with adding delimiters " to create new columns. This is in excel though but I'm not sure how you parse this data so might not work for you. Or str_replace() them and then str.split?