I have a json assigned to variable as:
var a = "[{a:123}]";
Now if I do a[0] it gives result as [. On doing a = JSON.parse(a) it gives error as Uncaught SyntaxError: Unexpected token a in JSON at position 2
How can i convert a into a = [{a:123}]; ?
The problem here is that you don't have a valid JSON.
Uncaught SyntaxError: Unexpected token a in JSON at position 2
This error complains about the character "a" which is not valid here. See http://www.json.org/
You could in theory achieve your goal by using eval but this is highly insecure because you can evaluate any code that is present in your string so I wouldn't recommend that.
You have to either make sure that the JSON you get is valid, or you may need to preprocess the string before passing it to JSON.parse if the format cannot be changed.
By the way, contrary to another answer here that was upvoted for some reason, there is no such thing as Array.parse:
$ node -e 'Array.parse()'
[eval]:1
Array.parse()
^
TypeError: Array.parse is not a function
See also:
You have to replace :
var a = "[{a:123}]";
by :
var a = "[{\"a\":123}]";
var a = '[{"a":123}]'it would work. Try using a JSON Validator