I expected active to become its own CSV header. It did not. The JSON converter keeps top-level keys only. A nested object is one cell of JSON text, with inner quotes doubled so the row stays valid CSV. Parsing and conversion stay in the browser. Nothing is uploaded.

What the sample actually prints

This is the Sample button array on the page:

[ { "id" : 1 , "name" : "Ada" , "role" : "engineer" , "meta" : { "active" : true } } , { "id" : 2 , "name" : "Linus" , "role" : "founder" , "meta" : { "active" : false } } ]

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CSV output:

id,name,role,meta 1,Ada,engineer,"{""active"":true}" 2,Linus,founder,"{""active"":false}"

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active sits inside meta , so it is not a header. An array value is also one cell. {"id":1,"tags":[]} converts to a tags cell of [] .

The same nest is not flat in TypeScript

TypeScript drafts from the first object only. Nested meta becomes a second interface.…