How can I parse a CSV string with embedded commas in quoted fields using regular expressions in JavaScript?

Regex-based CSV String Parsing

Problem Statement:

Parse a CSV string with commas embedded within quoted values, while ignoring commas outside quotes.

Solution Overview:**

To properly parse a CSV string that may contain quoted values with escaped characters, it's necessary to walk through the string character by character. Two regular expressions are employed:

CSV Validation Regex:

^\s*(?:'[^'\]*(?:\[\S\s][^'\]*)*'|"[^"\]*(?:\[\S\s][^"\]*)*"|[^,'"\s\]*(?:\s+[^,'"\s\]+)*)\s*(?:,\s*(?:'[^'\]*(?:\[\S\s][^'\]*)*'|"[^"\]*(?:\[\S\s][^"\]*)*"|[^,'"\s\]*(?:\s+[^,'"\s\]+)*)\s*)*$

This regex ensures that the input string follows the defined CSV format, where:

• Values can be single-quoted, double-quoted, or unquoted.
• Quoted values may contain escaped characters.
• Commas are used as separators.

Value Parsing Regex:

(?!\s*$)\s*(?:'([^'\]*(?:\[\S\s][^'\]*)*)'|"([^"\]*(?:\[\S\s][^"\]*)*)"|([^,'"\s\]*(?:\s+[^,'"\s\]+)*)|)\s*(?:,|$)

This regex extracts one value at a time from the CSV string, considering the same rules as the validation regex. It handles quoted values and removes escaped characters.

JavaScript Implementation:**

function CSVtoArray(text) {
    const re_valid = /^\s*(?:'[^'\]*(?:\[\S\s][^'\]*)*'|"[^"\]*(?:\[\S\s][^"\]*)*"|[^,'"\s\]*(?:\s+[^,'"\s\]+)*)\s*(?:,\s*(?:'[^'\]*(?:\[\S\s][^'\]*)*'|"[^"\]*(?:\[\S\s][^"\]*)*"|[^,'"\s\]*(?:\s+[^,'"\s\]+)*)\s*)*$/;
    const re_value = /(?!\s*$)\s*(?:'([^'\]*(?:\[\S\s][^'\]*)*)'|"([^"\]*(?:\[\S\s][^"\]*)*)"|([^,'"\s\]*(?:\s+[^,'"\s\]+)*))\s*(?:,|$)/g;
    // Return NULL if input string is not well formed CSV string.
    if (!re_valid.test(text)) return null;
    const a = [];                     // Initialize array to receive values.
    text.replace(re_value, // "Walk" the string using replace with callback.
        function(m0, m1, m2, m3) {
            // Remove backslash from \' in single quoted values.
            if      (m1 !== undefined) a.push(m1.replace(/\'/g, "'"));
            // Remove backslash from \" in double quoted values.
            else if (m2 !== undefined) a.push(m2.replace(/\"/g, '"'));
            else if (m3 !== undefined) a.push(m3);
            return ''; // Return empty string.
        });
    // Handle special case of empty last value.
    if (/,\s*$/.test(text)) a.push('');
    return a;
}

Example Usage:**

const csvString = "'string, duppi, du', 23, lala";
const result = CSVtoArray(csvString);
console.log(result); // ["string, duppi, du", "23", "lala"]

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