Eval ("(" +json object + ")")

var obj=eval ("(" +data+ ")");
Look at this one, you should think of the JSON data structure
"+ (JSON object name) +"
Since JSON starts and ends in the form of "{}", in JS, it is treated as a block of statements, so it must be coerced into an expression. Because consider it as a whole, so add the bracket
("+ (JSON object name) +")
Next, to use the JSON data as a whole with eval for JavaScript translation, the outside should add a pair of quotation marks, that is
Eval ("(" + (JSON object name) + ")")
And then assign it to a JSON object, which is
var obj=eval ("(" +data+ ")");