Question

IN my web service,I return one json object in the method:

{name:'xx'}

I use the ajax to send the request,then parse them using the ‘eval’

onComplete:function(req){
  var data=eval(req.responseText);
  //do something according data
}

However,I can not get the ‘data’.

When I retrun the following string:

[{name:'xx'}]

It worked,and I get the ‘data’ as an array.

Through google,I know that it is caused by the ‘{‘ in the return string.

So I wonder if there is no way to retrun a json object ?

Answer 1

Have a read of this blog post on JSON hijacking. The author explains the issue your running into

You might have seen code like the following when related to JSON:

eval('('+JSON_DATA+')');

Notice the beginning and ending parenthesis, this is to force
JavaScript to execute the data as an object not a block statement
mentioned above. If JavaScript did attempt to execute JSON data
without the parenthesis and the JSON data did in fact begin with “{”
then a syntax error would occur because the block statement would be
invalid.

…more info on why…

Rather than adding () around your JSON response, you should be using JSON.parse or $.parseJSON like gion_13 has said. Eval isn’t the way to go.

Also, like quentin said in the comments, you need to change the JSON you’re returning as it’s invalid. You need to quote your key as well as your value.