index.js

'use strict';

var ESCAPE_CODES = {
	0: 0,
	1: 22,
	2: 22,
	3: 23,
	4: 24,
	7: 27,
	8: 28,
	9: 29,
	30: 39,
	31: 39,
	32: 39,
	33: 39,
	34: 39,
	35: 39,
	36: 39,
	37: 39,
	38: 39,
	90: 39,
	40: 49,
	41: 49,
	42: 49,
	43: 49,
	44: 49,
	45: 49,
	46: 49,
	48: 49,
	47: 49
};

function wrapAnsi(pair) {
	var result = '';
	var tmpCode;

	while ((tmpCode = pair.pop())) {
		result += '\u001b[' + tmpCode + 'm';
	}

	return result;
}

module.exports = function (str, start, end) {
	var originalString = str.replace(/\u001b\[.*?m/g, '');
	start = (start < 0) ? 0 : start;

	if (end === undefined) {
		end = originalString.length;
	}
	end = (originalString.length < end) ? originalString.length : end;
	var ansiRegex = new RegExp(/\u001b\[(\d+).*?m/g);
	var ansiResult = ansiRegex.exec(str);
	var ansiCursor = 0;
	var stringCursor = 0;
	var tmpCursor;
	var resultString = '';
	var pair = [];

	if (!ansiResult) {
		return str.substring(start, end);
	}

	if (start === end) {
		return '';
	}

	do {
		if (ansiCursor < ansiResult.index) {
			tmpCursor = stringCursor + (ansiResult.index - ansiCursor);

			if (stringCursor >= start && tmpCursor <= end) {
				resultString += originalString.substring(stringCursor, tmpCursor);
			} else if (stringCursor <= start && tmpCursor >= start && tmpCursor <= end) {
				resultString += originalString.substring(start, tmpCursor);
			} else if (stringCursor <= end && tmpCursor >= end && stringCursor >= start) {
				resultString +=
					(originalString.substring(stringCursor, end));
				break;
			} else if (stringCursor <= start && tmpCursor >= end) {
				resultString +=
					(originalString.substring(start, end));
				break;
			}
		}

		stringCursor += (ansiResult.index - ansiCursor);
		if (stringCursor >= end) {
			break;
		}

		if (ESCAPE_CODES[ansiResult[1]]) {
			pair.push(ESCAPE_CODES[ansiResult[1]]);
		} else {
			var index = pair.indexOf(ansiResult[1]);
			pair.splice(index, 1);
		}
		resultString += ansiResult[0];
		ansiCursor = ansiRegex.lastIndex;
		if (stringCursor <= start && pair.length === 0) {
			resultString = '';
		}
	} while ((ansiResult = ansiRegex.exec(str)) !== null);

	resultString += wrapAnsi(pair);
	if (tmpCursor <= end) {
		if (tmpCursor > start) {
			resultString += originalString.substring(tmpCursor, end);
		} else {
			resultString = originalString.substring(start, end);
		}
	}

	return resultString;
};