JSON and eval

Question

In Metro what is the recommended method of converting a JSON string into a JavaScript object? Do we still have to use 'eval' (after verifying that string is valid) or we can use Windows.Data.Json WinRT object? In MSDN I didnt see JavaScript usage of Windows.Data.Json hence the question.

evals() historically in jscript.dll was one of the slowest operations (in terms of CPU cycles). Has that changed in Windows 8, given that many Metro apps will use JavaScript and rely heavily on JSON?

 

Answer 1

 

This works well for me:

	 var myObject = JSON.parse(myJSONstring);

and reverse:

	var myJSONstring = JSON.stringify(myObject);

Answer 2

The SDK samples I've seen use JSON.parse as jrboddie suggests. the JSON.* APIs are supported natively in the Metro style app environment.

Note that the Windows.Data.Json API in WinRT is actually not made available to apps written in JavaScript because JSON.* is already here. You'll find that the WinRT APIs are oriented around strongly-typed languages like C#, VB, and C++, and for which other APIs aren't available.

Answer 3

Thanks  jrboddie and Kraig

Answer 4

One thing to keep in mind with using JSON.parse/JSON.stringify -- JavaScript Date objects will serialize to a string but they will not revive as Dates. So if you take a simple object that has a date as one of its properties and do a stringify and then a parse you will end up with a string instead of a Date.

To work around this you can pass a custom reviver function to JSON.parse() and there just so happens to be the exact code to do this on the MSDN documentation page for JSON.parse:

http://msdn.microsoft.com/en-us/library/cc836466(VS.85).aspx

 

Cheers,

-Jeff

Answer 5

I was unable to find a "parse" method anywhere in Windows.Data.Json, either in JsonValue or in JsonObject. I was able to construct a JsonObject from a string, but that pre-supposes I know I've got an object in the JSON string. Where do I find the parse method? Thanks.