'use strict';

// MODULES //

var isString = require( '@stdlib/utils/is-string' ).isPrimitive;
var replace = require( '@stdlib/string/replace' );


// VARIABLES //

var RE = /[-\/\\^$*+?.()|[\]{}]/g; // eslint-disable-line no-useless-escape


// MAIN //

/**
* Escapes a regular expression string.
*
* @param {string} str - regular expression string
* @throws {TypeError} first argument must be a string primitive
* @returns {string} escaped string
*
* @example
* var str = rescape( '[A-Z]*' );
* // returns '\\[A\\-Z\\]\\*'
*/
function rescape( str ) {
	var len;
	var s;
	var i;

	if ( !isString( str ) ) {
		throw new TypeError( 'invalid input argument. Must provide a regular expression string. Value: `' + str + '`.' );
	}
	// Check if the string starts with a forward slash...
	if ( str[ 0 ] === '/' ) {
		// Find the last forward slash...
		len = str.length;
		for ( i = len-1; i >= 0; i-- ) {
			if ( str[ i ] === '/' ) {
				break;
			}
		}
	}
	// If we searched the string to no avail or if the first letter is not `/`, assume that the string is not of the form `/[...]/[gimy]`:
	if ( i === void 0 || i <= 0 ) {
		return replace( str, RE, '\\$&' );
	}
	// We need to de-construct the string...
	s = str.substring( 1, i );

	// Only escape the characters between the `/`:
	s = replace( s, RE, '\\$&' );

	// Reassemble:
	str = str[ 0 ] + s + str.substring( i );

	return str;
} // end FUNCTION rescape()


// EXPORTS //

module.exports = rescape;

'use strict';

// MODULES //

var isString = require( '@stdlib/utils/is-string' ).isPrimitive;


// VARIABLES //

var RE = /[-\/\\^$*+?.()|[\]{}]/g; // eslint-disable-line no-useless-escape


// MAIN //

/**
* Escapes a regular expression string.
*
* @param {string} str - regular expression string
* @throws {TypeError} first argument must be a string primitive
* @returns {string} escaped string
*
* @example
* var str = rescape( '[A-Z]*' );
* // returns '\\[A\\-Z\\]\\*'
*/
function rescape( str ) {
	var len;
	var s;
	var i;

	if ( !isString( str ) ) {
		throw new TypeError( 'invalid input argument. Must provide a regular expression string. Value: `' + str + '`.' );
	}
	// Check if the string starts with a forward slash...
	if ( str[ 0 ] === '/' ) {
		// Find the last forward slash...
		len = str.length;
		for ( i = len-1; i >= 0; i-- ) {
			if ( str[ i ] === '/' ) {
				break;
			}
		}
	}
	// If we searched the string to no avail or if the first letter is not `/`, assume that the string is not of the form `/[...]/[gimy]`:
	if ( i === void 0 || i <= 0 ) {
		return str.replace( RE, '\\$&' );
	}
	// We need to de-construct the string...
	s = str.substring( 1, i );

	// Only escape the characters between the `/`:
	s = s.replace( RE, '\\$&' );

	// Reassemble:
	str = str[ 0 ] + s + str.substring( i );

	return str;
} // end FUNCTION rescape()


// EXPORTS //

module.exports = rescape;

Use prototype replace method