I use JLD2.jl to store simulation results which I find pretty convenient.
I wonder if there is a plan to add a preview/explorer feature for this type of file in vscode.
Json files are nicer for a having a quick look on their content but, AFAIU, this format is not really suitable to store large numerical results (like large arrays of floats).
Any thought ?
No plans, but I really like the idea. Feel free to open a feature request.
Dedicated support for JLD2 sounds great.
I think, a lot should already be possible with HDF5 Preview - Visual Studio Marketplace
since JLD2 files is really just HDF5 with a few extras (mapping to julia structs).
Done 
Yes, I even try to change the jld2 extension to hdf5 and open it with this vscode extension but it does not work as is.
Is anyone interested in collaborating on this?
I could build a minimal version of JLD2 that would allow extracting metadata and maybe reading standard data types. It would need a vscode extension frontend to wrap it.
I know that @ffevotte made some experiment on this topic.
I made experiments building a standalone Electron app to preview the contents of JLD2 files. But I think this is mostly different from building a VScode extension.
The julia-vscode related open issue is here:
Also post my github comment here:
GitHub - silx-kit/vscode-h5web: VSCode extension to explore and visualize HDF5 files H5web is a lovely HDF5 reader in vscode that I’ve frequently used. It supports many formats other than .h5 and is open to extensions. I wonder if anyone can work on the JLD2 reader with h5web?