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One early version of the express-fileupload module in Node.js accepted JSON input along with the file upload, and used a general "object merge" algorithm to update the state in-memory.

express-fileupload.js
JavaScript 
function processNested(data) {
  if (!data || data.length < 1) return {};

  let d = {},
    keys = Object.keys(data);

  for (let i = 0; i < keys.length; i++) {
    let key = keys[i],
      value = data[key],
      current = d,
      keyParts = key.replace(new RegExp(/\[/g), '.').replace(new RegExp(/\]/g), '').split('.');

    for (let index = 0; index < keyParts.length; index++) {
      let k = keyParts[index];
      if (index >= keyParts.length - 1) {
        current[k] = value;
      } else {
        if (!current[k]) current[k] = !isNaN(keyParts[index + 1]) ? [] : {};
        current = current[k];
      }
    }
  }

  return d;
}