function forEach( str, options, clbk ) {
	var thisArg;
	var nargs;
	var opts;
	var cb;
	if ( !isString( str ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', str ) );
	}
	opts = {
		'mode': 'grapheme'
	};
	nargs = arguments.length;
	if ( nargs === 2 ) {
		cb = options;
		options = null;
	} else if ( nargs === 3 ) {
		if ( isPlainObject( options ) ) {
			cb = clbk;
		} else {
			cb = options;
			options = null;
			thisArg = clbk;
		}
	} else { // nargs === 4
		if ( !isPlainObject( options ) ) {
			throw new TypeError( format( 'invalid argument. Options argument must be an object. Value: `%s`.', options ) );
		}
		cb = clbk;
		thisArg = arguments[ 3 ];
	}
	if ( !isFunction( cb ) ) {
		throw new TypeError( format( 'invalid argument. Callback argument must be a function. Value: `%s`.', cb ) );
	}
	if ( options ) {
		if ( hasOwnProp( options, 'mode' ) ) {
			opts.mode = options.mode;
			if ( !isMode( opts.mode ) ) {
				throw new TypeError( format( 'invalid option. `%s` option must be one of the following: "%s". Value: `%s`.', 'mode', MODES.join( '", "' ), opts.mode ) );
			}
		}
	}
	FCNS[ opts.mode ]( str, cb, thisArg );
	return str;
}
Invokes a function for each character in a string.

@param {string} str - input string
@param {Options} [options] - options
@param {string} [options.mode="grapheme"] - type of "character" over which to iterate (must be either `grapheme`, `code_point`, or `code_unit`)
@param {Function} clbk - function to invoke
@param {*} [thisArg] - execution context
@throws {TypeError} first argument must be a string
@throws {TypeError} callback argument must be a function
@throws {TypeError} options argument must be an object
@throws {TypeError} must provide valid options
@returns {string} input string

@example
function log( value, index ) {
    console.log( '%d: %s', index, value );
}

forEach( 'Hello', log );