I am using jquery in my web application. There we use the below eval method.
var json = eval('(' + data + ')');
After googling I found eval method used above converts json data to javascript object. But what does that syntax means ? why it has to be enclosed within ('(' ')') parenthesis. Please help me in understanding.
Use () to enclose data is to prevent {} to be parsed as a block.
var json = eval('{}'); // the result is undefined
var json = eval('({})'); // the result is the empty object.
var json = eval('{"a": 1}'); // syntax error
var json = eval('({"a": 1})'); // the result is object: {a: 1}
But you should not use eval to parse json data.
Use var json = JSON.parse(data); or some library functions instead.
{a: 1} is not valid JSON. That is actually parsed as a label a for an empty expression 1 in a block.
JSON.parse is what you should use, except for IE<9 (doesn't support JSON out of the box. Not to worry: $.parseJSON(data); is X-browser, and since you're using jQuery already, why not use the latter?Don't use eval to parse json. Since you're using jQuery, use $.parseJSON(data). What if data contained window.close()?
WRT to the parentheses, you can see a comment explaining them in douglas crockford's json2.js:
// In the third stage we use the eval function to compile the text into a // JavaScript structure. The '{' operator is subject to a syntactic ambiguity // in JavaScript: it can begin a block or an object literal. We wrap the text // in parens to eliminate the ambiguity.
