Eval converted to JSON object __js

When Eval converts to a JSON object, why add parentheses, var dataobj=eval ("(" +data+ ")");

Note: sometimes without () is also normal to perform, sometimes there will be conversion errors, suggestions are added

The purpose of parentheses is to force the Eval function to force an expression in parentheses (expression) into an object when processing JavaScript code instead of executing as a statement (statement). For example, an object literal {}, if the outer bracket is not added, Eval recognizes the curly braces as the opening and closing tags of the JavaScript code block, then {} will be considered to have executed an empty statement. So the following two execution results are different:

Alert (eval ("{}")); return undefined
alert (eval ({}));//return Object[object]