Making a javascript string sql friendly

Question

It turns out that mysql_real_escape_string() is pretty trivial. According to the documentation:

mysql_real_escape_string() calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: \x00, \n, \r, \, ', " and \x1a.

Sounds pretty simple, actually. You could do something like this:

function mysql_real_escape_string (str) {
    return str.replace(/[\0\x08\x09\x1a\n\r"'\\\%]/g, function (char) {
        switch (char) {
            case "\0":
                return "\\0";
            case "\x08":
                return "\\b";
            case "\x09":
                return "\\t";
            case "\x1a":
                return "\\z";
            case "\n":
                return "\\n";
            case "\r":
                return "\\r";
            case "\"":
            case "'":
            case "\\":
            case "%":
                return "\\"+char; // prepends a backslash to backslash, percent,
                                  // and double/single quotes
            default:
                return char;
        }
    });
}

NOTE: I haven't run this through any sort of unit test or security test, but it does seem to work -- and, just as an added bonus, it escapes tabs, backspaces, and '%' so it can also be used in LIKE queries, as per OWASP's recommendations (unlike the PHP original).

I do know that mysql_real_escape_string() is character-set-aware, but I'm not sure what benefit that adds.

There's a good discussion of these issues over here.

Learnt the hard way that passing numbers to this function causes the whole process it is used in to die quietly. So I add a little test:

function mysql_real_escape_string (str) {
    if (typeof str != 'string')
        return str;

    return str.replace(/[\0\x08\x09\x1a\n\r"'\\\%]/g, function (char) {
        switch (char) {
            case "\0":
                return "\\0";
            case "\x08":
                return "\\b";
            case "\x09":
                return "\\t";
            case "\x1a":
                return "\\z";
            case "\n":
                return "\\n";
            case "\r":
                return "\\r";
            case "\"":
            case "'":
            case "\\":
            case "%":
                return "\\"+char; // prepends a backslash to backslash, percent,
                                  // and double/single quotes
        }
    });
}

For anyone who is coming to this answer from 2018 onwards it is also worth noting that a number of javascript database frameworks now contain a connection.escape method.

For instance:

var mysql = require('mysql')

var connection = mysql.createConnection( // your connection string here 

var query = "SELECT THING FROM THING WHERE FRED= " + connection.escape( your_string_here ); 

In case someone is looking for, the escapeString() in CUBRID RDBMS works as follows:

var _escapeString = function (val) {
  val = val.replace(/[\0\n\r\b\t\\'"\x1a]/g, function (s) {
    switch (s) {
      case "\0":
        return "\\0";
      case "\n":
        return "\\n";
      case "\r":
        return "\\r";
      case "\b":
        return "\\b";
      case "\t":
        return "\\t";
      case "\x1a":
        return "\\Z";
      case "'":
        return "''";
      case '"':
        return '""';
      default:
        return "\\" + s;
    }
  });

  return val;
};

This is an excerpt from CUBRID Node.js driver.

Using arrays instead of a case statement:

var regex = new RegExp(/[\0\x08\x09\x1a\n\r"'\\\%]/g)
var escaper = function escaper(char){
    var m = ['\\0', '\\x08', '\\x09', '\\x1a', '\\n', '\\r', "'", '"', "\\", '\\\\', "%"];
    var r = ['\\\\0', '\\\\b', '\\\\t', '\\\\z', '\\\\n', '\\\\r', "''", '""', '\\\\', '\\\\\\\\', '\\%'];
    return r[m.indexOf(char)];
};

//Implementation
"Some Crazy String that Needs Escaping".replace(regex, escaper);

Solution that works also for Frontend projects

Install sqlstring (a library maintained by mysqljs):

npm install sqlstring --save-dev  

if you use TypeScript you can also install the typings:

npm install @types/sqlstring --save-dev  

Then use it:

import { escape } from 'sqlstring';

const escapedString = escape(`it's going to be escaped!`);