function percentEncode( str ) {
	if ( !isString( str ) ) {
		throw new TypeError( format( 'invalid argument. Must provide a string. Value: `%s`.', str ) );
	}
	return base( str );
}
Percent-encodes a UTF-16 encoded string according to [RFC 3986][1].

[1]: https://tools.ietf.org/html/rfc3986#section-2.1

@param {string} str - string to percent-encode
@throws {TypeError} must provide a string
@returns {string} percent-encoded string

@example
var str1 = 'Ladies + Gentlemen';

var str2 = percentEncode( str1 );
// returns 'Ladies%20%2B%20Gentlemen'