--- /dev/null
+var isObject = require('./isObject'),
+ isRegExp = require('./isRegExp'),
+ stringSize = require('./internal/stringSize'),
+ stringToArray = require('./internal/stringToArray'),
+ toInteger = require('./toInteger'),
+ toString = require('./toString');
+
+/** Used as default options for `_.truncate`. */
+var DEFAULT_TRUNC_LENGTH = 30,
+ DEFAULT_TRUNC_OMISSION = '...';
+
+/** Used to match `RegExp` flags from their coerced string values. */
+var reFlags = /\w*$/;
+
+/** Used to compose unicode character classes. */
+var rsAstralRange = '\\ud800-\\udfff',
+ rsComboMarksRange = '\\u0300-\\u036f\\ufe20-\\ufe23',
+ rsComboSymbolsRange = '\\u20d0-\\u20f0',
+ rsVarRange = '\\ufe0e\\ufe0f';
+
+/** Used to compose unicode capture groups. */
+var rsZWJ = '\\u200d';
+
+/** Used to detect strings with [zero-width joiners or code points from the astral planes](http://eev.ee/blog/2015/09/12/dark-corners-of-unicode/). */
+var reHasComplexSymbol = RegExp('[' + rsZWJ + rsAstralRange + rsComboMarksRange + rsComboSymbolsRange + rsVarRange + ']');
+
+/**
+ * Truncates `string` if it's longer than the given maximum string length.
+ * The last characters of the truncated string are replaced with the omission
+ * string which defaults to "...".
+ *
+ * @static
+ * @memberOf _
+ * @category String
+ * @param {string} [string=''] The string to truncate.
+ * @param {Object} [options] The options object.
+ * @param {number} [options.length=30] The maximum string length.
+ * @param {string} [options.omission='...'] The string to indicate text is omitted.
+ * @param {RegExp|string} [options.separator] The separator pattern to truncate to.
+ * @returns {string} Returns the truncated string.
+ * @example
+ *
+ * _.truncate('hi-diddly-ho there, neighborino');
+ * // => 'hi-diddly-ho there, neighbo...'
+ *
+ * _.truncate('hi-diddly-ho there, neighborino', {
+ * 'length': 24,
+ * 'separator': ' '
+ * });
+ * // => 'hi-diddly-ho there,...'
+ *
+ * _.truncate('hi-diddly-ho there, neighborino', {
+ * 'length': 24,
+ * 'separator': /,? +/
+ * });
+ * // => 'hi-diddly-ho there...'
+ *
+ * _.truncate('hi-diddly-ho there, neighborino', {
+ * 'omission': ' [...]'
+ * });
+ * // => 'hi-diddly-ho there, neig [...]'
+ */
+function truncate(string, options) {
+ var length = DEFAULT_TRUNC_LENGTH,
+ omission = DEFAULT_TRUNC_OMISSION;
+
+ if (isObject(options)) {
+ var separator = 'separator' in options ? options.separator : separator;
+ length = 'length' in options ? toInteger(options.length) : length;
+ omission = 'omission' in options ? toString(options.omission) : omission;
+ }
+ string = toString(string);
+
+ var strLength = string.length;
+ if (reHasComplexSymbol.test(string)) {
+ var strSymbols = stringToArray(string);
+ strLength = strSymbols.length;
+ }
+ if (length >= strLength) {
+ return string;
+ }
+ var end = length - stringSize(omission);
+ if (end < 1) {
+ return omission;
+ }
+ var result = strSymbols
+ ? strSymbols.slice(0, end).join('')
+ : string.slice(0, end);
+
+ if (separator === undefined) {
+ return result + omission;
+ }
+ if (strSymbols) {
+ end += (result.length - end);
+ }
+ if (isRegExp(separator)) {
+ if (string.slice(end).search(separator)) {
+ var match,
+ substring = result;
+
+ if (!separator.global) {
+ separator = RegExp(separator.source, toString(reFlags.exec(separator)) + 'g');
+ }
+ separator.lastIndex = 0;
+ while ((match = separator.exec(substring))) {
+ var newEnd = match.index;
+ }
+ result = result.slice(0, newEnd === undefined ? end : newEnd);
+ }
+ } else if (string.indexOf(separator, end) != end) {
+ var index = result.lastIndexOf(separator);
+ if (index > -1) {
+ result = result.slice(0, index);
+ }
+ }
+ return result + omission;
+}
+
+module.exports = truncate;