What’s the best AI code assistant for large JavaScript/TypeScript projects?

When working with large JavaScript or TypeScript codebases , the ideal AI code assistant needs strong multi-file context awareness , deep understanding of type definitions (TS AST/symbols), and robust refactoring capabilities rather than just single-line tab-completions.

The top options excel in different areas for large-scale JS/TS projects:

1. Cursor (The Best Dedicated AI Code Editor)

• What it is: A fork of VS Code built from the ground up to integrate AI natively.
• Why it shines for large JS/TS projects: Cursor indexes your entire codebase locally into an embeddings database. When you use its Composer or Chat feature (Ctrl/Cmd + I ), it doesn't just guess based on the current file; it searches across the whole project to trace imports, understand complex monorepo boundaries (e.g., Turborepo, Nx), and see how changes in a shared utility or type definition will impact other modules.
• Model flexibility: Allows seamless switching between top-tier reasoning models like Claude 3.5 Sonnet and GPT-4o , which excel heavily at complex TypeScript generics and refactoring.
• Downside: It is a separate fork/application , meaning you have to migrate your VS Code settings over (though it’s a 1-click process).

2. Sourcegraph Cody (Best for Deep Enterprise Code Intelligence)

• What it is: An AI assistant powered by Sourcegraph’s enterprise-grade code search.
• Why it shines for large JS/TS projects: Cody excels when your project spans multiple microservices, massive enterprise monorepos, or deeply nested legacy code where standard IDE indexing struggles. It uses precise code intelligence (Code Graph) to pull contextually relevant snippets from across your entire organization's repositories, ensuring the AI understands custom internal libraries and complex dependency trees.
• Downside: Setup is heavier, especially if you aren’t already leveraging Sourcegraph infrastructure across your team.

3. GitHub Copilot with Copilot Workspace / Chat (Best Native VS Code / JetBrains Experience)

• What it is: Microsoft/GitHub's flagship assistant , deeply integrated into standard IDEs via extensions.
• Why it shines for large JS/TS projects: If you prefer staying strictly inside vanilla VS Code or JetBrains without using a fork, Copilot has closed the gap significantly with multi-file edit capabilities and agent-mode features. Its inline completions are fast, and it integrates tightly with GitHub PRs, issues, and workspace context.
• Downside: Historically weaker at autonomous, multi-file codebase-wide refactors compared to Cursor's Composer mode, though feature updates continue to narrow this gap.

Recommendation Summary

• Go with Cursor if you want the absolute best out-of-the-box experience for multi-file JavaScript/TypeScript refactoring, generating tests across files, and reasoning over a large directory structure.
• Stick with GitHub Copilot if your enterprise security rules mandate official standard extensions in vanilla VS Code or you want seamless integration with your GitHub workflows.
• Look at Sourcegraph Cody if you are dealing with multi-repo enterprise monsters where global code search context is vital.

To help narrow this down, could you tell me:

• Are you using a monorepo structure (like Nx, Turborepo, or Lerna)?
• Do you have any strict data privacy/enterprise compliance requirements that restrict cloud-based AI tools?

For a large JavaScript/TypeScript project (React, Next.js, Node, monorepos, large codebases), the best choice depends on how you work, but the current leaders are:

🥇 Best overall: Cursor

Best if you spend most of your day in VS Code.

Why it fits large JS/TS projects:

• Strong codebase indexing and project context
• Excellent multi-file edits (e.g., “convert this Redux slice to Zustand across the app”)
• Good TypeScript awareness
• Lets you review diffs directly in the editor
• Familiar VS Code workflow

Best for:

• Full-stack TypeScript apps
• React/Next.js projects
• Daily feature work
• Refactors where you want control

Many comparisons currently put Cursor as the strongest all-around IDE experience, especially for developers who want AI deeply integrated into editing.

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🥈 Best for huge refactors: Anthropic Claude Code

Best when the task is “understand this entire repo and make a major change.”

Examples:

• “Migrate this 200-file Express API to Fastify”
• “Find all usages of this deprecated API and update them”
• “Add tests for this subsystem”
• “Debug why this monorepo build fails”

Strengths:

• Very good long-context reasoning
• Strong at architecture-level changes
• Works well with terminal workflows, git, tests, and migrations

Tradeoff:

• Less convenient for constant inline coding than an IDE assistant.

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🥉 Best enterprise default: GitHub GitHub Copilot

Best if your team already lives in GitHub.

Strengths:

• Excellent IDE coverage
• Strong pull request / GitHub workflow integration
• Easier for companies to approve
• Good autocomplete and everyday assistance

Tradeoff:

• For deep multi-file reasoning, many developers find Cursor or Claude Code stronger.

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My recommendation by scenario

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The setup I’d choose for a serious TS codebase

1. Cursor as the daily editor

• autocomplete
• component work
• small/medium refactors

2. Claude Code for “architect mode”

• repo-wide changes
• debugging
• migrations
• test generation

3. Keep normal engineering safeguards:

• require tests before merging
• review every diff
• avoid letting agents rewrite core architecture without checkpoints

For a large JavaScript/TypeScript codebase, I’d currently start with Cursor, and add Claude Code if you regularly do repository-wide changes.

For a large JavaScript/TypeScript codebase, my pick right now is Cursor—with Claude Code as the strongest alternative if you prefer a terminal-first workflow.

My ranking

1. Cursor — best overall

• Excellent at navigating large repos and making coordinated multi-file changes.
• Its Agent can search the codebase, edit multiple files, run commands, fix errors, and execute tests.
• Particularly good for JS/TS: TypeScript IntelliSense, automatic imports, ESLint integration, and project-aware completions are all well supported.
• Its semantic codebase indexing is specifically designed to make large repositories searchable; Cursor reports improved agent accuracy from semantic search.
• You can also choose among multiple underlying models rather than being locked to one provider.

2. Claude Code — best for difficult refactors

• I'd choose this if your work looks like: "Understand this entire monorepo, migrate this architecture, update all callers, run tests, and fix whatever breaks."
• It's particularly strong for autonomous, multi-step terminal work. Independent 2026 comparisons also tend to put it near the top for complex multi-file reasoning.
• The downside is that it's less of an integrated editor experience than Cursor.

3. GitHub Copilot — best conventional IDE choice

• Still the safest choice if you want to remain in VS Code/JetBrains and don't want to change your development environment.
• Its biggest advantage is breadth of IDE integration and GitHub workflow integration.
• I'd choose it for a team that values familiarity and enterprise integration over maximum agentic capability.

4. Windsurf — worth considering

• Good agentic editor, but I would personally put Cursor ahead for a large TS/JS project.

The important distinction

For a 10,000+ file monorepo, I wouldn't optimize primarily for autocomplete quality. I'd optimize for:

codebase retrieval → architectural reasoning → multi-file edits → test execution → iterative debugging

That's where Cursor and Claude Code pull ahead of traditional "AI autocomplete" assistants. Current independent evaluations similarly find Cursor and Claude Code strongest on complex multi-file work.

What I'd actually use

If I were starting a large TypeScript project today:

Cursor + its Agent + a strong model would be my default.

I'd configure project rules covering things like:

• package boundaries
• TypeScript strictness
• architecture conventions
• testing requirements
• preferred libraries
• generated-code directories
• commands for lint/typecheck/test/build

Then use Plan Mode for architectural changes rather than letting the agent immediately start editing. Cursor explicitly supports researching the repo, producing an implementation plan, and waiting for approval before making changes.

For particularly nasty migrations or debugging sessions, I'd bring in Claude Code alongside Cursor rather than treating them as mutually exclusive.

Bottom line: Cursor = best all-around AI environment for a large JS/TS project. Claude Code = best specialist for deep autonomous refactoring/debugging. Copilot = best if you want minimal workflow disruption.

If you tell me roughly how big the repo is (e.g. 500k vs 5M lines), whether it's a monorepo, and whether you're using VS Code or JetBrains, I can give you a much more specific recommendation.

For large JavaScript and TypeScript projects, the "best" assistant comes down to deep codebase indexing (understanding how a massive web of imports, types, and monorepos fit together) and multi-file editing capability.

Large JS/TS codebases choke simple autocomplete tools because the AI needs to understand the AST (Abstract Syntax Tree), type definitions across packages, and indirect dependencies.

The top-tier choices for large-scale JS/TS development stand out for distinct reasons:

1. Cursor (The Best AI-First IDE)

• What it is: A fork of VS Code built completely around AI, supporting models like Claude 3.5 Sonnet and GPT-4o.
• Why it shines for large JS/TS projects: Cursor’s codebase indexing creates a local vector embedding of your entire project. When you ask it to refactor a deeply nested TypeScript interface or track down where a Redux action or Next.js API route is consumed across 50 files, it actually knows the project topology. Its Composer feature can cleanly write and apply multi-file edits simultaneously, handling complex imports and renaming constraints without breaking your type safety.
• Best for: Developers who want an all-in-one IDE experience with superior multi-file refactoring.

2. Claude Code (The Best Terminal/Agentic Assistant)

• What it is: Anthropic’s official agentic coding tool that runs in your command line.
• Why it shines for large JS/TS projects: Powered by top-tier reasoning models, Claude Code has direct read/write/execute access to your terminal and file system. For large projects, you can tell it to "find all unused exports in the packages/utils directory and safely remove them/update tests," and it will run tsc , check linting errors, inspect the files iteratively, and fix its own mistakes.
• Best for: Complex, multi-step refactors, running test suites autonomously, and deep architectural changes in monorepos.

3. Continue (The Best Open-Source/Customizable Option)

• What it is: An open-source autopilot and sidebar extension for VS Code and JetBrains.
• Why it shines for large JS/TS projects: If your enterprise codebase has strict data privacy rules or you want to hook up specific local/hosted models (like Gemini 1.5 Pro or local Llama variants with massive context windows), Continue lets you configure the exact embeddings and LLM backend you want. You can point it at custom retrieval-augmented generation (RAG) setups to index massive monorepos.
• Best for: Teams with strict compliance/privacy needs or those wanting deep customization over their toolchain.

4. GitHub Copilot (The Best Lightweight Inline Assistant)

• What it is: The incumbent extension deeply integrated into standard VS Code.
• Why it shines for large JS/TS projects: Copilot’s inline autocomplete ("ghost text") is fast and unobtrusive. While its chat and multi-file context understanding historically lagged behind Cursor, its Workspace features have gotten better at pulling in broader project context.
• Best for: Fast inline tab-completions and developers who cannot switch away from official VS Code.

Summary Recommendation

• Use Cursor if you want a seamless daily driver that excels at understanding your entire TypeScript type system and editing across multiple files at once.
• Pair it or swap to Claude Code if you have heavy, repetitive, or complex project-wide refactoring tasks that benefit from an autonomous terminal agent.

To help narrow this down, tell me:

• Are you working in a monorepo (e.g., Turborepo, Nx, Lerna) or a standard single-repo?
• Do you have strict data privacy/compliance constraints that prevent cloud-indexing your code?

For a large JavaScript/TypeScript codebase, my pick right now is Cursor, with Claude Code as the strongest alternative.

My ranking

🥇 Cursor — best overall

For a big TS monorepo, I'd start here. Cursor's Agent can explore the repository, make multi-file changes, run commands, and iterate on errors. Its documentation specifically has guidance for large codebases and recommends using its planning/Ask mode before implementation/Agent mode.

It's particularly good for:

• React / Next.js / Node / NestJS / monorepos
• Understanding unfamiliar parts of a large repository
• Cross-file refactors
• Following existing project patterns
• Keeping you inside the editor rather than bouncing between IDE and terminal
• Using different models depending on the task

For JS/TS specifically, Cursor has strong framework and TypeScript support, automatic imports, lint-error iteration, and documentation injection.

If I were starting a 500k+ LOC TypeScript project today, this is what I'd try first.

🥈 Claude Code — best for serious refactoring

Claude Code is arguably better when the task sounds like:

"Trace how authentication works throughout this repo, migrate it to the new API, update all affected tests, run the test suite, and fix anything that breaks."

It operates as an agent: searches the codebase, edits files, executes commands, runs tests, and loops until the task is complete.

I'd choose Claude Code over Cursor when the work itself is more important than the editor experience—large migrations, architectural refactors, debugging complicated interactions, repository-wide changes, etc.

A really good setup is actually:

Cursor for everyday development + Claude Code for heavyweight tasks.

🥉 GitHub Copilot

Copilot remains a very good choice if your organization is deeply invested in GitHub and VS Code/JetBrains. Its biggest advantage is low friction and excellent integration into an existing development workflow.

I'd pick it over Cursor if enterprise integration, standardized tooling, and GitHub workflows matter more than getting the most capable coding agent.

The important distinction

For a large project, don't optimize for autocomplete quality. Optimize for repository-level reasoning.

You want an assistant that can:

1. Find the relevant files without you feeding them one by one.
2. Understand dependencies between modules.
3. Make coordinated multi-file changes.
4. Run TypeScript, ESLint, tests, and builds.
5. Inspect failures and fix them.
6. Respect existing architectural conventions.

That's where Cursor and Claude Code pull ahead. Cursor's Agent, for example, has repository search, file editing, terminal execution, web access, and MCP integrations.

Bottom line:

• One tool: Cursor
• Best agent for big refactors: Claude Code
• Best enterprise/lowest-friction choice: GitHub Copilot
• Best power-user setup: Cursor + Claude Code

If you tell me roughly how big the repo is (LOC/files), whether it's a monorepo, and whether you use VS Code/JetBrains, I can give you a much more specific recommendation.

When working with large JavaScript or TypeScript codebases, traditional AI autocomplete falls short because it only looks at the current file . For massive monorepos or sprawling enterprise apps, you need an assistant with deep multi-file context , strong TypeScript type-awareness , and agentic refactoring capabilities.

The top-tier choices break down by how you prefer to work:

1. Cursor – Best AI-Native IDE for Multi-File Refactoring
   • Why it shines: Built as a fork of VS Code, Cursor indexes your entire project into a local vector embedding database. Its "Composer" feature allows you to execute simultaneous, multi-file code generation and refactoring across your entire TS/JS architecture in one go. It doesn't just guess the next line; it understands how your frontend components map to your backend types or services.
   • Best for: Developers who want a seamless GUI experience that feels like VS Code but thinks at the repository level.
2. Claude Code – Best Terminal-First Agent for Deep Codebase Reasoning
   • Why it shines: Anthropic’s official terminal agent combines massive context windows with high-level reasoning. It navigates complex directory structures, traces deep data flows across packages, runs your build or test commands locally, and handles massive multi-file overhauls directly from the shell. Using a CLAUDE.md file lets you hardcode your project’s strict TypeScript rules, testing commands, and architectural patterns into its persistent memory.
   • Best for: Senior developers and architects who are comfortable in the CLI and need an agent to trace deep bugs or execute complex system-wide migrations.
3. Sourcegraph Cody – Best for Massive Enterprise Codebases & Code Graph Search
   • Why it shines: Leveraging Sourcegraph ’s industry-leading code intelligence and search graph, Cody has an unmatched global map of dependencies, imports, and symbol definitions across hundreds of separate repositories. If your project spans multiple microservices or a sprawling enterprise monorepo where nobody knows where a function is defined, Cody's context retrieval cuts through the noise.
   • Best for: Large engineering teams working across massive, distributed repositories where global code search is the main bottleneck.
4. GitHub Copilot (with Agent Mode / GPT-5) – Best for Low-Friction IDE Integration
   • Why it shines: If you refuse to leave standard VS Code or JetBrains, Copilot remains the most ubiquitous choice. With recent upgrades bringing advanced agent capabilities and heavier model integrations, its inline autocomplete and chat features handle routine boilerplate exceptionally well, though it still requires more manual guidance than Cursor or Claude Code on massive architectural refactors.
   • Best for: Developers who want reliable, everyday inline suggestions without adopting a separate custom editor.

To help narrow down the ideal choice, tell me:

• Are you working in a monorepo , a standard single repo , or multi-service microservices?
• Do you prefer staying inside a GUI editor like VS Code/Cursor or working via the terminal?

When working with large, complex JavaScript/TypeScript projects, simple inline autocompletion isn’t enough. You need an assistant with deep codebase-wide indexing , an understanding of complex type hierarchies/imports, and the ability to execute multi-file refactors safely.

The landscape breaks down into a few clear winners depending on how you like to work:

1. Cursor (Best Overall AI-First IDE)

• What it is: A standalone IDE (forked from VS Code) built from the ground up to be AI-native.
• Why it shines for large JS/TS repos: Cursor continuously indexes your entire repository locally. When you ask it to change a shared TypeScript interface or a core Redux/Zustand store, its Composer mode can accurately find, edit, and verify updates across dozens of interconnected files at once rather than just guessing inside the file you currently have open.
• Model flexibility: Lets you seamlessly route requests to top-tier reasoning models like Claude 4.5/4.6 Sonnet or GPT-5.
• Best for: Day-to-day feature development and sweeping multi-file refactors where keeping track of TS types across folders gets overwhelming.

2. Claude Code (Best Terminal-Native Agent)

• What it is: Anthropic’s official terminal-driven coding agent.
• Why it shines for large JS/TS repos: It runs directly in your shell, handles git workflows natively, and leverages an expansive context window. It excels at architectural reasoning, running test suites, tracking down deep-seated bugs across a massive monorepo, and executing complex, multi-step migration tasks. It also features a reliable checkpoint system so you can easily revert changes if an agentic run goes sideways.
• Best for: Senior engineers who love command-line workflows, massive legacy codebases, and handling large-scale migrations.

3. Windsurf (Best Alternative AI IDE)

• What it is: An AI-native IDE (also built on a VS Code base) powered by the Cascade engine.
• Why it shines for large JS/TS repos: It offers a flow very similar to Cursor, maintaining deep repository context while generally offering a more generous tier or aggressive pricing. Its "Supercomplete" and multi-step agent flows feel exceptionally smooth when spinning up new boilerplate or mapping components to a large backend schema.
• Best for: Developers looking for Cursor-level multi-file capability with a slightly different pricing/feature balance.

4. GitHub Copilot / Copilot Workspace (Best Traditional Plugin)

• What it is: The classic IDE extension supporting VS Code, JetBrains, and others.
• Why it shines for large JS/TS repos: If your enterprise or team has strict compliance rules prohibiting specialized forks like Cursor, Copilot is the gold standard. While its codebase context features historically lagged behind dedicated AI editors, its deep integration into the GitHub ecosystem and mature, low-latency inline autocompletion make it a dependable baseline.
• Best for: Environments with strict corporate governance policies or developers who just want fast, lightweight inline ghost-text without switching editors.

Quick Recommendation

• If you want a seamless graphical experience that rewrites 15 TypeScript files at the click of a button, use Cursor.
• If you prefer working in the command line and turning loose a powerful agent on a massive, gnarly repository, use Claude Code.
• If you are restricted by corporate policy , stick with GitHub Copilot.

If you want to narrow this down, tell me:

• Are you working in a monorepo or a standard multi-service repo?
• Do you have strict data privacy/enterprise requirements that limit your choice of tools?

I can give you a more tailored recommendation.

For large JavaScript/TypeScript codebases, my pick in 2026 is Cursor, with Claude Code as the strongest alternative—and for some teams, the best setup is actually both.

My ranking

🥇 Cursor — best overall

For a big TypeScript monorepo, I'd start with Cursor.

Its Agent mode can search the codebase, modify multiple files, execute commands, and fix resulting errors. docs.cursor.com More importantly, Cursor has semantic codebase indexing specifically designed to help agents find relevant code in large repositories.

That's particularly useful for tasks like:

"Trace how authentication works across the API and frontend, then migrate it from X to Y."

rather than:

"Write this function."

Cursor is especially good at:

• Large TypeScript monorepos
• React/Next.js projects
• Cross-package refactors
• Finding existing patterns and reusing them
• Understanding unfamiliar code
• Iterative edit → test → fix workflows

Cursor itself recommends using Ask for planning/exploration and Agent for implementation, and breaking very large changes into smaller chunks.

🥈 Claude Code — arguably better for the hardest work

If you don't mind working from a terminal, Claude Code is extremely strong.

It can read your codebase, edit files, run commands, execute tests, and iterate on the results.

I particularly prefer it for things like:

• Major architectural refactors
• Dependency migrations
• Debugging complicated interactions
• "Figure out why this happens" problems
• Large changes where you want the AI to investigate before touching code
• Git/CI/build/test workflows

The distinction I'd make is:

Cursor = better AI development environment
Claude Code = better autonomous coding agent

There's considerable overlap, though.

🥉 GitHub Copilot

Copilot is still the sensible choice if your team is deeply invested in GitHub + VS Code/JetBrains and doesn't want everyone moving to a new editor.

Its biggest advantage isn't necessarily raw coding ability—it's integration and low friction.

For a huge codebase where you're doing sophisticated multi-file changes all day, however, I'd personally choose Cursor or Claude Code.

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What I'd actually use

For a serious JS/TS project, I'd use:

Cursor + Claude Code

Use Cursor for your normal development loop:

understand code
    ↓
plan change
    ↓
edit files
    ↓
run tests
    ↓
review diff

Then use Claude Code when you encounter something unusually complicated:

"Find every place this abstraction is used."
"Why does this race condition happen?"
"Migrate this entire subsystem."
"Analyze the architecture before proposing a fix."

That's not redundant—the two interfaces encourage somewhat different workflows.

One important caveat

Don't choose based solely on advertised "context window" size. For huge repositories, retrieval quality, codebase search, ability to run/test code, and how well the agent maintains a coherent plan matter more than being able to shove the entire repository into a prompt. Cursor's own large-codebase guidance emphasizes scoped context and breaking large changes into manageable chunks.

Bottom line: If you want one tool, I'd choose Cursor. If you're willing to use two, Cursor + Claude Code is my favorite setup for a large TypeScript/JavaScript codebase in 2026.

For large JavaScript and TypeScript codebases—where understanding deep type systems, complex component trees, and multi-file ripple effects matters more than basic autocompletion—the "best" AI assistant depends heavily on how you prefer to work (via a graphical IDE, a terminal agent, or a deep code intelligence engine).

The top tools specifically suited for large, type-heavy JS/TS projects break down as follows:

• Cursor (Best IDE Experience)
  • Why it shines: Built as a fork of VS Code, Cursor embeds AI directly into your editor environment rather than treating it as a sidebar plugin. For multi-file TypeScript refactors, its Composer and Plan Mode excel at tracing imports, updating Zod schemas or tRPC contracts, and modifying related files simultaneously while keeping your local type-checker happy.
  • Best for: Developers who want an all-in-one IDE with smooth inline edits, codebase-wide type inference, and the flexibility to route to top-tier frontier models.
• Claude Code (Best Terminal-First Agent)
  • Why it shines: Anthropic’s command-line agentic tool operates directly inside your repository. It stands out in large codebases due to its superior reasoning with complex type systems, generics, and strict TypeScript configurations (strict: true ). By initializing a CLAUDE.md memory file in your project root, you can hardcode your architecture rules, build commands, and testing scripts so Claude never loses sight of project conventions.
  • Best for: Developers doing heavy refactoring, architectural restructuring, or bug-hunting who are comfortable running terminal commands and reviewing automated Git commits.
• Sourcegraph Cody (Best for Deep Code Intelligence & Cross-Repo Context)
  • Why it shines: Cody leverages Sourcegraph's industry-standard code search and graph-based indexing. In massive enterprise monorepos or multi-repo microservice environments, it maps out semantic dependencies across thousands of files far better than standard local RAG (Retrieval-Augmented Generation) setups.
  • Best for: Enterprise teams managing giant, sprawling JS/TS repositories or multi-repository architectures that require deep global context.
• GitHub Copilot (Best for Lightweight, Integrated Autocomplete)
  • Why it shines: While it trails dedicated agentic tools in multi-file refactoring reasoning, GitHub Copilot remains the most widely adopted and frictionless option. Its inline tab-completions and workspace chat integrate smoothly into standard VS Code and JetBrains ecosystems, benefiting from broad ecosystem maturity and strict enterprise compliance approvals.
  • Best for: Developers who primarily want fast, predictable line-and-block completions without leaving standard enterprise-approved IDEs.

To help narrow down the ideal choice, tell me:

• Are you working in a monorepo or a standard single-repository project?
• Do you prefer staying inside a graphical IDE like VS Code/Cursor or working via the terminal?

For large JavaScript/TypeScript codebases, my pick in 2026 is Cursor—with Claude Code as the strongest companion for really large refactors.

My ranking

Why Cursor wins: it combines an AI-native editor with codebase-wide semantic search, multi-file agents, and access to multiple frontier models. Cursor specifically says its indexing is designed for repositories with tens of thousands of files, and its current product supports models from Anthropic, OpenAI, Gemini and others.

For a big TS monorepo, that matters more than raw autocomplete quality. You want the assistant to understand relationships like:

React component → hook → service → API client → schema → tests → shared package

rather than just predict the next few lines.

When I'd choose Claude Code instead

If your work is mostly "take this 50-file subsystem and refactor/migrate/debug it", I'd seriously consider Claude Code. Independent 2026 comparisons consistently find it particularly strong for large multi-file changes and codebase reasoning, though its terminal-first workflow is less convenient for everyday editing.

The setup I'd personally use

Cursor + Claude Code

• Cursor: everyday coding, navigation, autocomplete, targeted edits, reviewing diffs.
• Claude Code: major refactors, migrations, debugging, understanding unfamiliar subsystems, running tests/builds and iterating.
• GitHub: PR/review workflow.

That two-tool approach is increasingly common because an IDE assistant and a terminal agent excel at somewhat different jobs.

Bottom line: If you want to install one tool today for a large JS/TS project, I'd choose Cursor. If you tell me whether you're using VS Code, WebStorm, or another IDE, and roughly how big the repo is (e.g. 100k vs. 1M+ LOC), I can give you a more specific recommendation.