>);

// Use that data.

print

'Number of JSON keys:

${jsonData.length}

);

In Flutter, you can also use the compute function 
to spin up an isolate to run a callback function:

final

jsonData

await

compute

getNumberOfKeys

jsonString

);

In this case, the callback function is a top-level
function as shown below:

Map

String

dynamic

getNumberOfKeys

String

jsonString

return

jsonDecode

jsonString

);