How to download Bitcoin block headers from Blockchain.info and save to file? I am just developing and testing Bitcoin mining application in plain Javascript
(slow but can be run off-line).

To test it to work correctly I need to download Bitcoin block headers
from Blockchain.info , 6 input parameters .

Are you aware how to call Blockchain API 
https://blockchain.info/api/blockchain_api

I don't use Bitcoin address, no other mining app, just need to download
a number block headers from hashed blocks.

Any idea, demo, example or csv file coming with 6 input parameters
as described in Bitcoin hashing algorithm

https://en.bitcoin.it/wiki/Block_hashing_algorithm
You can download the blockchain headers from here. The data is binary packed, but can be deserialized easily enough. You seem to be trying to solo mine, which is a bad idea at the best of times, let alone with JavaScript. You also seems to be trying to build a SPV client. An easier way would just be to use https://blockchain.info/latestblock to get the lastblock hash and use that.