如何从客户端JS文件中的数组中的多个对象中提取所需的键值对？

Question

I am required to extract desired key-values from a large .js file essentially containing an array of objects with fixed defined keys in json format by uploading it on the client-side.

I want to extract desired keys and values from each object. But the problem is that the file is 2+ GB in size and can't be uploaded all at once. So I need to at best split the file into small chunks and extract the required keys' values.

The .js file looks like the following, and let say I want to extract only b and d keys' values from each object.

var data = [{
  "a": "...",
  "b": [{
    "b-1": "...",
    "b-2": 3,
    "b-3": {"b-3-1": "..."}
  }, {...}, {...}],
  "c": false,
  "d": 25,
  ...
}, ..., {...}] 

I've read about FileReader and Blob Web APIs but don't know which one to use and how so in such a way that when splitting it into small chunks each chunk carries an entire object.

Please kindly help me on this problem.

Answer 1

What you need is a streaming JSON parser for Node, eg

• https://www.npmjs.com/package/JSONStream
• https://www.npmjs.com/package/stream-json
• https://www.npmjs.com/package/json-stream

If this is a one-of-job you may want to look into jq , (it's like sed for JSON data - you can use it to slice and filter data) eg piping data in and out of it (or you could automate it as well)

cat file.json | jq '.a' | less

See: https://shapeshed.com/jq-json/