JavaScript backslash in variables is causing an error

Question

In Javascript  when I put a backslash in some variables like   var ttt    aa          var ttt    aa           Javascript shows an error   If I try to restrict user in entering this character  I also get an error      aaa          indexOf         -1    Restricting backslashes from user input is not a good strategy  because you have to show an annoying message to the user    Why am I getting an error with backslash

User · Answer

The jsfiddle link to where i tried out your query http   jsfiddle net A8Dnv 1  its working fine   Imrul as mentioned you are using C  on server side and you dont mind that either  http   msdn microsoft com en-us library system text regularexpressions regex escape aspx

User · Answer

You have to escape each   to be      var ttt    aa                 Updated  I think this question is not about the escape character in string at all  The asker doesn t seem to explain the problem correctly      because you had to show a message to user that user can t give a name which has     character    I think the scenario is like   var user input name   document getElementById  the name   value    Then the asker wants to check if user input name contains any      If so  then alert the user   If user enters  aa       in HTML input box  then if you alert user input name   you will see  aaa        You don t need to escape  i e  replace     to be      in JavaScript code  When you do escaping  that is because you are trying to make of a string which contain special characters in JavaScript source code  If you don t do it  it won t be parsed correct  Since you already get a string  you don t need to pass it into an escaping function  If you do so  I am guessing you are generating another JavaScript code from a JavaScript code  but it s not the case here   I am guessing asker wants to simulate the input  so we can understand the problem  Unfortunately  asker doesn t understand JavaScript well  Therefore  a syntax error code being supplied to us   var ttt    aa          Hence  we assume the asker having problem with escaping   If you want to simulate  you code must be valid at first place   var ttt    aa             lt - This is correct    var ttt    aa            lt - This is not   alert ttt      You will see  aa       in dialog  which is what you expect  right    Now  you only need to do is  var user input name   document getElementById  the name   value  if  user input name indexOf        gt   0       There is a     in the string   alert     is not allowed to be used        User reads    is not allowed to be used    do something else          Edit  I used    to quote text to be shown  so it would be less confused than using

User · Answer

You may want to try the following  which is more or less the standard way to escape user input   function stringEscape s        return s   s replace     g         replace   n g    n   replace   t g    t   replace   v g    v   replace    g        replace    g        replace    x00- x1F x80- x9F  g hex    s      function hex c    var v    0  c charCodeAt 0  toString 16   return    x  v substr v length-2         This replaces all backslashes with an escaped backslash  and then proceeds to escape other non-printable characters to their escaped form  It also escapes single and double quotes  so you can use the output as a string constructor even in eval  which is a bad idea by itself  considering that you are using user input   But in any case  it should do the job you want

User · Answer

The backslash   is reserved for use as an escape character in Javascript   To use a backslash literally you need to use two backslashes

User · Answer

If you want to use special character in javascript variable value  Escape Character     is required   Backslash in your example is special character  too   So you should do something like this   var ttt    aa                -- gt           or  var ttt    aa            -- gt         But Escape Character not require for user input   When you press   in prompt box or input field then submit  that means single

User · Answer

The backslash     is an escape character in Javascript  along with a lot of other C-like languages   This means that when Javascript encounters a backslash  it tries to escape the following character  For instance   n is a newline character  rather than a backslash followed by the letter n    In order to output a literal backslash  you need to escape it  That means    will output a single backslash  and      will output two  and so on   The reason  aa       doesn t work is because the backslash escapes the    which will print a literal quote   and thus your string is not properly terminated  Similarly   aa         won t work  because the last backslash again escapes the quote   Just remember  for each backslash you want to output  you need to give Javascript two

[javascript] JavaScript backslash (\) in variables is causing an error

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