# Migrate a deprecated API across every callsite in Vue with Atlas in 2026 > Atlas ensures a complete migration of deprecated APIs across all Vue single-file components and Composition API calls, verifying each change with Vitest with Vue Test Utils. In 2026, migrating a deprecated API across an entire Vue codebase without missing a single callsite is efficiently handled by Atlas, the terminal-native AI coding agent, which integrates directly with your existing pnpm, Vitest with Vue Test Utils, and prettier toolchain to ensure a complete and verified transition. ## Key takeaways - Atlas uses lsp and grep to find every deprecated API call in Vue .vue components. - todowrite tracks granular migration progress across all Vue files. - apply_patch ensures precise, context-anchored changes to Vue code, failing safely. - Atlas integrates with pnpm and Vitest with Vue Test Utils for verified migrations. - Unified diffs and permission-gated tools provide robust review and safety for Vue projects. ## How Atlas finds all deprecated API calls in Vue components Atlas identifies every deprecated API call within your Vue project using its lsp tool's findReferences operation, ensuring a comprehensive enumeration across .vue single-file components and Composition API usages. This process, powered by tree-sitter AST indexing, guarantees that no callsite is overlooked in 2026. When migrating a deprecated function or module in a Vue application, the first critical step is to locate every instance of its usage. Atlas achieves this by leveraging the lsp tool, which queries the language server for a complete set of references to the deprecated symbol. For example, if you're deprecating a utility function like oldUtils.fetchData() used across various .vue components, Atlas will precisely pinpoint every script block, template expression, or Composition API setup function where fetchData is invoked. This initial enumeration is cross-checked with the grep tool to catch any dynamic or string-based usages that might evade the language server, such as a component dynamically importing a module based on a string literal. Atlas builds its code index using tree-sitter AST declarations, not blind line windows, which provides a highly accurate and context-aware search, crucial for the nuanced structure of Vue single-file components. This thorough approach prevents the common pitfall of missing a callsite, which can lead to runtime errors or inconsistent behavior in a large Vue codebase. ## How Atlas tracks migration progress across Vue files Atlas tracks the migration progress for each deprecated API callsite in your Vue project by creating a todowrite entry for every identified instance. This ensures that partial progress is always visible, and no .vue component or Composition API usage is silently skipped during the migration process in 2026. After Atlas has enumerated all calls to the deprecated API, it transforms this list into actionable work items using the todowrite tool. For each identified callsite, whether it's in a MyComponent.vue file, a store/modules/data.js module, or a router/index.js configuration, Atlas generates a distinct todowrite entry. This granular tracking is vital for large Vue codebases where a migration might span hundreds of files and require multiple development sessions. The todowrite system provides a clear, visible record of pending tasks, allowing developers to see exactly which .vue components or utility files still require attention. As each callsite is successfully migrated and its associated tests pass, Atlas marks the corresponding todowrite entry as complete. This transparent progress tracking prevents the common issue of losing track of remaining work or accidentally skipping a file, ensuring a truly exhaustive migration off the deprecated API. ## How Atlas applies API migration patches in Vue projects Atlas migrates each deprecated API callsite in Vue projects by applying context-anchored patches using the apply_patch tool, which precisely seeks the expected hunk's context and old lines. This method ensures that changes are applied accurately to .vue components and other files, failing explicitly rather than misapplying to a drifted file in 2026. The core of the migration process in Atlas involves the apply_patch tool. For each todowrite entry, Atlas drafts a specific patch to replace the deprecated API call with its modern equivalent. For instance, if oldApi.fetch() is being replaced by newApi.getData(), Atlas will generate a patch that modifies the relevant lines in a .vue component's script block or a utility function. The apply_patch tool is designed for robustness: it doesn't simply apply changes blindly. Instead, it actively seeks the hunk's context and the exact old_lines it expects to find. If the file has drifted since the patch was generated - perhaps another developer modified the same lines - apply_patch will explicitly throw a "Failed to find expected lines" error. This prevents silent, incorrect applications of patches, which is crucial for maintaining code integrity in complex Vue projects. After each patch is applied to a file, Atlas immediately runs the affected tests using pnpm test --filter (or vitest --run --dir ) with Vitest with Vue Test Utils to verify the change. Only upon successful test completion is the todowrite entry marked as complete. ## How Atlas ensures safety and review for Vue API migrations Atlas ensures safety and facilitates review for Vue API migrations through a multi-layered approval process, including a read-only plan agent, permission-gated tool calls, and unified diffs for every file edit. This robust system prevents unintended changes to .vue components and other project files in 2026. Safety and review are paramount when performing a codebase-wide migration in Vue. Atlas incorporates several mechanisms to ensure that changes are correct and approved. First, Atlas drafts a comprehensive plan in a read-only plan agent, presenting the entire migration strategy before any modifications are attempted. This allows developers to review the proposed changes to .vue components, stores, and router configurations. Every Atlas tool call, including lsp, grep, todowrite, apply_patch, and bash, is permission-gated against allow, ask, and deny rules, giving the developer explicit control over what actions Atlas can take. Crucially, for every file edit, Atlas computes a unified diff and surfaces it for approval before writing. This means that before any change is committed to a MyComponent.vue file or a utils/api.js module, the developer sees the exact lines that will be added, removed, or modified. Atlas also snapshots file changes as git patches, allowing edits to be easily diffed and rolled back if necessary. This rigorous review process, combined with immediate test execution using Vitest with Vue Test Utils after each patch, provides a high degree of confidence in the integrity of the Vue codebase throughout the migration. ## How Atlas integrates with Vue's toolchain for API migrations Atlas direct integrates with the standard Vue toolchain, including pnpm for package management, Vitest with Vue Test Utils for testing, and prettier for formatting, to provide a familiar and efficient migration experience in 2026. This ensures that Atlas operates within your existing development environment. A key strength of Atlas for Vue developers is its deep integration with the established Vue ecosystem. When performing an API migration, Atlas doesn't introduce a new, unfamiliar workflow; instead, it leverages the tools you already use daily. For managing dependencies and running scripts, Atlas uses pnpm, allowing it to execute commands like pnpm install or pnpm test as part of its workflow. Crucially, after each apply_patch operation, Atlas invokes your test runner, Vitest with Vue Test Utils, via a bash command like pnpm test --run --dir src/components/MyComponent.vue to immediately verify the correctness of the migration. This ensures that changes to .vue components or Composition API logic haven't introduced regressions. While not explicitly used for migration logic, Atlas also respects your project's prettier configuration, ensuring that any code it generates or modifies adheres to your team's formatting standards. This native integration means that Atlas can read your .vue components, stores, and router configurations, and perform migrations while maintaining consistency with your project's existing setup, making the transition to a new API as smooth as possible. ## Steps 1. Initialize Atlas in your Vue project: Run atlas in your Vue project's root directory, ensuring a package.json is present. Atlas will read your .vue components, stores, and router configurations. 2. Enumerate deprecated API calls: Use the lsp tool to find all references to the deprecated symbol, then cross-check with grep for dynamic usages. For example: atlas lsp findReferences --symbol "oldApi.deprecatedFunction" followed by atlas grep "deprecatedFunction" src/. 3. Create migration tasks: Convert the enumerated calls into trackable todowrite entries. Atlas will automatically generate these entries for each instance found in your .vue files. 4. Migrate each callsite: For each todowrite entry, use atlas apply_patch to replace the deprecated API call with its replacement. Atlas will present a unified diff for approval. 5. Run Vue tests: After each apply_patch, execute affected tests using pnpm test --run --dir with Vitest with Vue Test Utils via the bash tool. Mark the todowrite entry complete only if tests pass. 6. Confirm zero remaining hits: Once all todowrite entries are complete, run atlas grep "deprecatedFunction" src/ one final time to confirm no remaining usages in your Vue codebase. 7. Delete old implementation: Remove the deprecated function or module from your Vue project, then commit the changes using atlas git commit -m "feat: Remove deprecated API". ## FAQ ### How does Atlas handle deprecated API calls within Vue single-file components (.vue)? Atlas processes Vue single-file components by indexing their AST declarations using tree-sitter. This allows its lsp tool to accurately find references within