Navigation Features

Relevant source files

• src/compiler/binder.ts
• src/compiler/checker.ts
• src/compiler/commandLineParser.ts
• src/compiler/core.ts
• src/compiler/diagnosticMessages.json
• src/compiler/emitter.ts
• src/compiler/moduleNameResolver.ts
• src/compiler/moduleSpecifiers.ts
• src/compiler/parser.ts
• src/compiler/program.ts
• src/compiler/resolutionCache.ts
• src/compiler/scanner.ts
• src/compiler/sys.ts
• src/compiler/types.ts
• src/compiler/utilities.ts
• src/harness/client.ts
• src/harness/fourslashImpl.ts
• src/harness/fourslashInterfaceImpl.ts
• src/harness/harnessLanguageService.ts
• src/server/editorServices.ts
• src/server/project.ts
• src/server/protocol.ts
• src/server/scriptInfo.ts
• src/server/scriptVersionCache.ts
• src/server/session.ts
• src/server/utilities.ts
• src/services/codefixes/importFixes.ts
• src/services/completions.ts
• src/services/exportInfoMap.ts
• src/services/findAllReferences.ts
• src/services/goToDefinition.ts
• src/services/importTracker.ts
• src/services/navigateTo.ts
• src/services/navigationBar.ts
• src/services/patternMatcher.ts
• src/services/services.ts
• src/services/types.ts
• src/services/utilities.ts
• src/testRunner/unittests/tsserver/exportMapCache.ts
• tests/baselines/reference/api/typescript.d.ts
• tests/baselines/reference/tsserver/exportMapCache/invalidates-the-cache-when-a-file-is-opened-with-different-contents.js
• tests/cases/fourslash/fourslash.ts
• tests/cases/fourslash/server/completionsOverridingMethodCrash2.ts

This page documents the navigation services provided by the TypeScript language service: the navigation bar (file structure outline), outlining spans (code folding), navigate-to (cross-file symbol search), and core go-to-definition and implementation features. These services enable IDEs to provide structured views and rapid movement through the codebase.

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Navigation Bar

The navigation bar gives editors a hierarchical outline of the symbols defined in a source file. It is surfaced through two entry points in the language service:

Function	Return type	Description
getNavigationBarItems	NavigationBarItem[]	Flat list suitable for a two-level primary/secondary navbar menu
getNavigationTree	NavigationTree	Full recursive tree of symbols

Both are implemented in src/services/navigationBar.ts

Internal Representation: NavigationBarNode

Before converting to the public NavigationBarItem or NavigationTree types, the service builds an intermediate tree of NavigationBarNode objects.

The additionalNodes field holds extra source nodes that were merged into a single logical entry (e.g., an interface declared in multiple blocks, or an ES5 class where the constructor and prototype assignments are separate).

Sources: src/services/navigationBar.ts161-168

Tree Construction

The service builds the tree by visiting AST nodes recursively. A module-level stack (parentsStack) tracks the current parent node to avoid deep recursion overhead.

Navigation Bar Build Pipeline

Sources: src/services/navigationBar.ts171-229 src/services/navigationBar.ts143-154

ES5 Class Merging

JavaScript code using the ES5 prototype pattern produces separate AST nodes. The navigation bar merges these into a single class-like entry using addTrackedEs5Class and tryMergeEs5Class.

Sources: src/services/navigationBar.ts246-253 src/services/navigationBar.ts617-724

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Outlining Spans

The outlining service computes collapsible regions (code folding). It is exposed via collectElements in src/services/outliningElementsCollector.ts

Field	Type	Description
textSpan	TextSpan	The collapsible range
hintSpan	TextSpan	The range shown when collapsed (e.g., the header line)
bannerText	string	Text shown in collapsed state (default: "...")
kind	OutliningSpanKind	Code, Comment, Imports, or Region

Sources: src/services/outliningElementsCollector.ts59-65

Collection Pipeline

The collector runs two independent passes: one for node-based structures (functions, blocks) and one for comment-based regions (#region).

Sources: src/services/outliningElementsCollector.ts59-136 src/services/outliningElementsCollector.ts138-162

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Navigate-To (Symbol Search)

Navigate-To allows cross-file searching for named declarations. It uses a fuzzy matching engine implemented in src/services/patternMatcher.ts

Search Flow

The service iterates through all files in the Program, retrieving named declarations via sourceFile.getNamedDeclarations().

Navigate-To Search Flow

Sources: src/services/navigateTo.ts42-66 src/services/navigateTo.ts110-128

Pattern Matcher

The matcher splits the search string into segments (by .) and chunks (by word boundaries). It supports exact, prefix, substring, and camelCase matches.

Sources: src/services/patternMatcher.ts17-22 src/services/patternMatcher.ts72-141

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Go-To-Definition and Implementation

These features resolve the location of a symbol's declaration or its concrete implementations.

Go-To-Definition

Implemented in src/services/goToDefinition.ts this feature resolves the symbol at a specific position and returns its declaration sites.

1. Token Identification: getTouchingPropertyName or getTouchingToken finds the node at the cursor src/services/services.ts125-126
2. Symbol Resolution: The TypeChecker is used to find the Symbol associated with the node src/compiler/checker.ts125
3. Definition Mapping: The service maps the symbol's declarations to DefinitionInfo objects, including support for finding definitions in .d.ts files or original source via source maps src/services/services.ts53-54

Find Implementations

Exposed via getImplementationAtPosition, this feature specifically looks for overrides of class members or implementations of interface members.

• It uses the TypeChecker to navigate the inheritance hierarchy (getAnyBaseTypes) src/compiler/checker.ts34
• It identifies all classes or objects that implement a specific interface or override a virtual method src/services/services.ts140

Sources: src/services/goToDefinition.ts src/services/services.ts127 src/compiler/checker.ts125

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Integration with Language Service

The LanguageService interface in src/services/services.ts coordinates these features.

Method	Implementation File
getNavigationBarItems	src/services/navigationBar.ts
getNavigationTree	src/services/navigationBar.ts
getOutliningSpans	src/services/outliningElementsCollector.ts
getNavigateToItems	src/services/navigateTo.ts
getDefinitionAtPosition	src/services/goToDefinition.ts
getImplementationAtPosition	src/services/services.ts

Sources: src/services/services.ts212-280