nested object set and get // extract from lodash

object-get-set.js

/*
path access: object util get/set with path access

get(obj, path) => value of obj at path:
	expect(get({ a: 0 }, 'b[1].c')).toBe(null);
	expect(get({ b: [0, { c: 'CCC' }] }, 'b[1].c')).toBe('CCC');
set(obj, path, value) => new object updates object value at path
	expect(set({a: 0}, 'b.c', 1)).toMatchObject({ a:0, b: {c: 1} });
	expect(set({a: 0}, 'b.c', 2, (v) => v * 10).b.c).toBe(20);
	expect(set({ a: 0 }, 'b[1]', 1)).toMatchObject({ a:0, b: [undefined, 1] });
	expect(set({ a: [0] }, 'a[2]', 'VALUE')).toMatchObject({ a:[0, undefined, 'VALUE'] });
	expect(set({ a: [0] }, 'a[2].c', 'VALUE')).toMatchObject({ a:[0, undefined, {c: 'VALUE'}] });
set(obj, path, updater) => new object updates object with updater at path
*/

const reLeadingDot = /^\./;
const rePropName = /[^.[\]]+|\[(?:(-?\d+(?:\.\d+)?)|(["'])((?:(?!\2)[^\\]|\\.)*?)\2)\]|(?=(?:\.|\[\])(?:\.|\[\]|$))/g;
const reEscapeChar = /\\(\\)?/g;

const isNaN = (i) => i !== i
const isArr = (a) => a instanceof Array
const isArrIndex = (key) => !isNaN(parseInt(key, 10));

export function stringToPath(string) {
	const result = [];
	if (reLeadingDot.test(string)) {
		result.push('');
	}
	string.replace(rePropName, function(match, number, quote, string) {
		result.push(quote ? string.replace(reEscapeChar, '$1') : (number || match));
	});
	return result;
};

export function toPath(path) {
	return typeof path === 'string' ? stringToPath(path) : [].concat(path);
}

export function get(obj, path) {
	return stringToPath(path).reduce((memo, key) => {
		if (memo == null || !(key in memo)) return null;
		return memo[key];
	}, obj);
}

const isPositiveInteger = (n) => n >>> 0 === parseFloat(n); // 这个版本只支持最大到 4294967295( Math.pow(2,32) - 1) ) 的数值
// function isPositiveInteger(n) { // 这个版本能支持到 Number.MAX_VALUE
//   return 0 === n % (!isNaN(parseFloat(n)) && 0 <= ~~n);
// }
// 详细文档见 SO https://stackoverflow.com/questions/10834796/validate-that-a-string-is-a-positive-integer

function _set(obj, pathArr, value, customizer = r => r) {
  if (pathArr.length === 0) {
    return typeof value === 'function' ? value(obj) : value;
  }
  const firstKey = pathArr[0];
  if (typeof obj !== 'object') {
    obj = isPositiveInteger(firstKey) ? [] : {};
  }
  const val = _set(obj[firstKey], pathArr.slice(1), value, customizer);

  let next;
  if (Array.isArray(obj)) {
    next = [].concat(obj);
    next[firstKey] = val;
  } else {
    next = { ...obj, [firstKey]: val };
  }
  
  if (pathArr.length === 1) {
    return customizer(next, firstKey, obj);
  }
  return next;
}

export default function set(obj, path, value, customizer) {
  return _set(obj, toPath(path), value, customizer);
}