Parsing strings with JavaScript

parser.js

const arrow = (str, i) => str[i] === '-' && str[i+1] === '>';

const string = (c) => c === "'" || c === '"';

const comma = (c) => c === ',';

const opener = (c) => c === '(';

const closer = (c) => c === ')';

const parse = (i, str, result) => {

	let value = '';
	let quote = null;

	while (i < str.length) {

		// character reference
		let c = str[i];

		// enter level
		if (opener(c)) {

			let fn = [value.trim()];

			i = parse(i + 1, str, fn);

			result.push(fn);
			value = '';
		}

		// exit level
		else if (closer(c)) {

			if (value.trim().length) {
				result.push(value.trim());
			}

			return i+1;
		}

		// function names or arguments
		else {

			// we're in a string
			// as long as the exit has not been found add to value
			if (quote !== null && c !== quote) {

				// accept any value
				value += c;

			}
			// we've found the string exit
			else if (c === quote) {
				quote = null;
			}
			// we're not in a string and we found a string opener
			else if (string(c)) {
				quote = c;
			}
			// we're not in a string
			else {

				// we've found an arrow
				if (arrow(str, i)) {

					// we might have finished a function without parenthesis
					if (value.trim().length) {
						result.push([value.trim()]);
						value = '';
					}

					// skip two additional characters because arrow is of length 2 
					i+=2;
				}
				// we've reached an argument separator
				else if (comma(c)) {

					// push value
					if (value.trim().length) {
						result.push(value.trim());
					}
					value = '';

				}
				else {
					value += c;
				}
			}

			// next character
			i++;
		}
	}

	if (value.trim().length) {
		result.push([value.trim()]);
	}

	return i;
};

export const parseTransformChain = string => {
	let result = [];
	parse(0, string, result);
	return result;
};

patterns.js

"foo" 
// [["foo"]]

"foo -> bar" 
// [ ["foo"], ["bar"] ]

"foo(a, b)"
// [ ["foo", "a", "b"], ["bar"] ]

"foo(a, 'a, b')"
// [ ["foo", "a", "a, b"] ]

"foo -> bar(baz(a, b))" 
// [ ["foo"], ["bar", ["baz", "a", "b"] ] ]