[demo] deep freeze

deep-freeze.js

/* if 'use strict' mode, TypeErrors occurs*/

/**
 * freeze object deeply
 *
 * @param {{}} object
 */
const deepFreeze = (object) => {
  Object.freeze(object);

  for (const propKey in object) {
    const prop = object[propKey];

    const shouldContinue =
      !object.hasOwnProperty(propKey) ||
      typeof prop !== "object" ||
      Object.isFrozen(prop);

    if (shouldContinue) {
      continue;
    }

    deepFreeze(prop);
  }
};

/**
 * deep freeze object
 *
 * @type {{obj: {deep: string}, shallow: string}}
 */
const deepFreezeObj = {
  obj: {
    deep: "freeze!!",
  },
  shallow: "freeze!!",
};

/**
 * shallow freeze object
 *
 * @type {{obj: {deep: string}, shallow: string}}
 */
const shallowFreezeObj = {
  obj: {
    deep: "freeze!!",
  },
  shallow: "freeze!!",
};

deepFreeze(deepFreezeObj);
Object.freeze(shallowFreezeObj);

// try writing
deepFreezeObj.obj.deep = "change...";
deepFreezeObj.shallow = "change...";

shallowFreezeObj.obj.deep = "change...";
shallowFreezeObj.shallow = "change...";

// print
console.log(deepFreezeObj.obj.deep); // freeze!!
console.log(deepFreezeObj.shallow); // freeze!!

console.log(shallowFreezeObj.obj.deep); // change...
console.log(shallowFreezeObj.shallow); // freeze!!