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Problem solution · TypeScript

Make Object Immutable

Make Object Immutable: a TypeScript solution using depth-first search. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Depth-first search
Source
walkccc LeetCode Solutions
Length
50 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Depth-first search

For Make Object Immutable, the implementation follows one branch at a time, making it suitable for components, trees, backtracking, or dependency exploration.

  1. Define the state carried into one recursive or stack frame.
  2. Mark or choose the current state before exploring children.
  3. Combine child results or undo the choice when the branch finishes.

Code notes

  • 50 lines of TypeScript from the credited upstream file 2692.ts.
  • The implementation visibly relies on ordered lookup.
  • No explicit loop blocks detected.

Complexity

Count unique states for graph traversal; for backtracking, count the branching factor and maximum depth.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeMake Object Immutable · TypeScriptTypeScript
Use this to learn the idea, then write your own version.
type RecursiveHandler = {  set: <T extends object>(target: T, prop: string, value: any) => boolean;  get: <T extends object>(target: T, prop: string) => any;  apply: <T extends Function>(target: T, thisArg: any, argArray?: any) => any;}; function makeImmutable<T extends object | Function>(obj: T): T {  // a set of mutating array methods  const methods = new Set([    'pop',    'push',    'shift',    'unshift',    'splice',    'sort',    'reverse',  ]);   const handler: RecursiveHandler = {    // 'set' trap prevents modifications of the object properties.    set(target, prop, _) {      throw Array.isArray(target)        ? `Error Modifying Index: ${String(prop)}`        : `Error Modifying: ${String(prop)}`;    },    // 'get' trap returns object properties or creates new proxies for nested    // objects or functions    get(target, prop) {      // If the property is 'prototype', null, or not an object/function, return      // it directly. We exclude 'prototype' to avoid potential issues with      // inheritance Objects and functions are wrapped in a new proxy to      // preserve immutability at all depths.      const key = prop as keyof typeof target;      return prop === 'prototype' ||        target[key] === null ||        (typeof target[key] !== 'object' && typeof target[key] !== 'function')        ? target[key]        : new Proxy(target[key], this);    },    // 'apply' trap prevents call of mutating methods and apply function calls.    apply(target, thisArg, argumentsList) {      if (methods.has((target as any).name))        throw `Error Calling Method: ${(target as any).name}`;      return target.apply(thisArg, argumentsList);    },  };   return new Proxy(obj, handler) as T;}

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