lodash-at.js

function at(obj, path, val = undefined) {
  // If path is an Array, 
  if (Array.isArray(path)) {
    // it returns the mapped array for each result of the path
    return path.map((path) => at(obj, path, val));
  }
  // Uniting several RegExps into one
  const rx = new RegExp(
    [
      /(?:^(?:\.\s*)?([_a-zA-Z][_a-zA-Z0-9]*))/,
      /(?:^\[\s*(\d+)\s*\])/,
      /(?:^\[\s*'([^']*(?:\\'[^']*)*)'\s*\])/,
      /(?:^\[\s*"([^"]*(?:\\"[^"]*)*)"\s*\])/,
      /(?:^\[\s*`([^`]*(?:\\`[^`]*)*)`\s*\])/,
    ]
      .map((r) => r.source)
      .join("|")
  );
  let rm;
  while (rm = rx.exec(path.trim())) {
    // Matched resource
    let [rf, rp] = rm.filter(Boolean);
    // If no one matches found,
    if (!rm[1] && !rm[2]) {
      // it will replace escape-chars
      rp = rp.replace(/\\(.)/g, "$1");
    }
    // If the new value is set,
    if ("undefined" != typeof val && path.length == rf.length) {
      // assign a value to the object property and return it
      return (obj[rp] = val);
    }
    // Going one step deeper
    obj = obj[rp];
    // Removing a step from the path
    path = path.substr(rf.length).trim();
  }
  if (path) {
    throw new SyntaxError();
  }
  return obj;
}

// Test object schema
let o = { a: { b: [ [ { c: { d: { '"e"': { f: { g: "xxx" } } } } } ] ] } };

// Print source object
console.log(JSON.stringify(o));

// Set value
console.log(at(o, '.a["b"][0][0].c[`d`]["\\"e\\""][\'f\']["g"]', "zzz"));

// Get value
console.log(at(o, '.a["b"][0][0].c[`d`]["\\"e\\""][\'f\']["g"]'));

// Print result object
console.log(JSON.stringify(o));