Public Compiler API

Relevant source files

This page documents the public TypeScript compiler API exposed through the typescript npm package. It covers the primary programmatic entry points for invoking the compiler, inspecting ASTs, and performing semantic analysis. For information about the language service API (editor features like completions and refactorings), see Language Service. For details on tsserver and the JSON protocol used by editors, see Language Server.

Overview

The typescript package ships a single bundled module (lib/typescript.js) that exports everything under the ts namespace. The public surface is canonically defined in the generated declaration file at tests/baselines/reference/api/typescript.d.ts

The API has three main uses:

Use Case	Primary Entry Points
Full compilation (type-check + emit)	`createProgram`, `Program.emit`
Single-file parsing only	`createSourceFile`
Single-file transpilation (no type-check)	`transpileModule`
Editor / tooling integration	`createLanguageService`

High-Level Component Map

The diagram below maps user-facing API calls to the internal compiler components they drive.

Diagram: Public API Entry Points to Internal Components

Sources: src/compiler/program.ts328-340 src/services/services.ts1-360 tests/baselines/reference/api/typescript.d.ts1-50

Entry Point: `createProgram`

createProgram is the primary entry point for full compilations. It accepts either a list of root file names and options, or a CreateProgramOptions object.

createProgram(rootNames, options, host?, oldProgram?, configFileParsingDiagnostics?)
createProgram(options: CreateProgramOptions)

The returned Program object is the top-level handle for all subsequent operations. Its key methods are:

Method	Description
`getSourceFiles()`	Returns all `SourceFile` nodes in the program
`getSourceFile(fileName)`	Looks up a specific `SourceFile`
`getTypeChecker()`	Returns the `TypeChecker` for semantic queries
`emit(targetSourceFile?, writeFile?, ...)`	Runs the emitter; returns `EmitResult`
`getSyntacticDiagnostics(sourceFile?)`	Parse-level errors
`getSemanticDiagnostics(sourceFile?)`	Type-level errors
`getDeclarationDiagnostics(sourceFile?)`	Errors from `.d.ts` generation
`getCompilerOptions()`	Returns the active `CompilerOptions`
`getRootFileNames()`	Returns the initial root file list
`getResolvedModuleFromModuleSpecifier(...)`	Module resolution result

Sources: src/compiler/program.ts1-326 tests/baselines/reference/api/typescript.d.ts3200-3350

Entry Point: `createSourceFile`

createSourceFile(
    fileName: string,
    sourceText: string,
    languageVersionOrOptions: ScriptTarget | CreateSourceFileOptions,
    setParentNodes?: boolean,
    scriptKind?: ScriptKind
): SourceFile

Parses a single source text string into a SourceFile AST node without creating a full Program. Useful for tooling that only needs the parse tree.

setParentNodes — if true, sets the parent pointer on every AST node (required for many utilities)
scriptKind — controls parsing mode: TS, TSX, JS, JSX, JSON, etc.

Sources: src/compiler/parser.ts1-440 tests/baselines/reference/api/typescript.d.ts3380-3400

Entry Point: `transpileModule`

transpileModule(input: string, transpileOptions: TranspileOptions): TranspileOutput

Performs single-file TypeScript-to-JavaScript transpilation with no cross-file type checking. Significantly faster than createProgram for cases where semantic correctness is not needed. TranspileOptions accepts a compilerOptions object and an optional moduleName.

TranspileOutput contains:

outputText — the emitted JavaScript string
sourceMapText — optional source map JSON string
diagnostics — any syntactic errors encountered

Sources: tests/baselines/reference/api/typescript.d.ts3400-3430

Entry Point: `createLanguageService`

createLanguageService(
    host: LanguageServiceHost,
    documentRegistry?: DocumentRegistry,
    syntaxOnlyOrLanguageServiceMode?: boolean | LanguageServiceMode
): LanguageService

Creates an editor-facing LanguageService instance backed by a caller-supplied LanguageServiceHost. The host provides file contents, compiler options, and file system access incrementally. See Language Service for a full treatment of LanguageService capabilities.

Sources: src/services/services.ts1-360 src/services/types.ts1-100

`CompilerHost` Interface

CompilerHost is the file system and environment abstraction used by createProgram. Callers can supply a custom host to redirect file I/O (e.g. for in-memory compilation or virtual file systems).

Key required methods:

Method	Description
`fileExists(fileName)`	Check if a file exists
`readFile(fileName)`	Read file contents as a string
`getSourceFile(fileName, languageVersion, ...)`	Parse and return a `SourceFile`
`getDefaultLibFileName(options)`	Path to the default library (`lib.d.ts`)
`writeFile(fileName, data, ...)`	Write output files
`getCurrentDirectory()`	Current working directory
`getCanonicalFileName(fileName)`	Normalize file name casing
`useCaseSensitiveFileNames()`	Whether file names are case-sensitive
`getNewLine()`	Line ending string

A default host for Node.js is available via createCompilerHost(options).

Sources: src/compiler/types.ts5500-5600 tests/baselines/reference/api/typescript.d.ts3300-3380

The `Program` Object and Compilation Flow

Diagram: Program Lifecycle and Internal Calls

Sources: src/compiler/program.ts1-326 src/compiler/binder.ts1-310 src/compiler/checker.ts1-1155 src/compiler/emitter.ts1-430

AST Representation

`SourceFile`

A SourceFile is the root AST node for a single file. Key properties:

Property	Type	Description
`fileName`	`string`	Absolute file path
`text`	`string`	Full source text
`statements`	`NodeArray<Statement>`	Top-level statements
`languageVersion`	`ScriptTarget`	Target script version
`scriptKind`	`ScriptKind`	JS/TS/JSX variant
`isDeclarationFile`	`boolean`	Whether this is a `.d.ts` file
`referencedFiles`	`FileReference[]`	Triple-slash references
`diagnostics`	(internal)	Parse errors

`Node`

Every AST element implements the Node interface. The kind property is a SyntaxKind enum member that identifies the node type. The public API adds helper methods on Node instances returned by the language services layer (NodeObject in src/services/services.ts374-495):

Method	Description
`getSourceFile()`	Enclosing `SourceFile`
`getStart(sf?, includeJsDoc?)`	Start position (skipping trivia)
`getFullStart()`	Start position including leading trivia
`getEnd()`	End position
`getText(sf?)`	Source text substring
`getChildren(sf?)`	Child nodes including trivia tokens
`forEachChild(cb, cbArray?)`	Iterate direct children

`SyntaxKind` Enum

SyntaxKind is a large const enum (src/compiler/types.ts40-492) that assigns an integer to every possible node and token kind. Key ranges:

Range	Description
`Unknown` .. `EndOfFileToken`	Special/trivial tokens
`NumericLiteral` .. `NoSubstitutionTemplateLiteral`	Literal tokens
`OpenBraceToken` .. `CaretEqualsToken`	Punctuation and operators
`BreakKeyword` .. `DeferKeyword`	Keywords
`QualifiedName` .. `ImportType`	Type nodes
`SourceFile`	Source file root
`FirstJSDocNode` .. `LastJSDocNode`	JSDoc nodes

Sources: src/compiler/types.ts40-492 src/services/services.ts374-495

Semantic Model: `TypeChecker`

The TypeChecker is obtained from program.getTypeChecker(). It provides all semantic analysis queries. It is lazy — most analysis only occurs when a method is called.

Diagram: TypeChecker Key Methods and What They Return

`TypeChecker` Method Groups

Symbol queries:

Method	Description
`getSymbolAtLocation(node)`	Symbol for an identifier or declaration
`getSymbolsInScope(location, meaning)`	All symbols visible at a position
`getExportsOfModule(symbol)`	Exported symbols of a module
`getPropertiesOfType(type)`	Property symbols of an object type
`getAliasedSymbol(symbol)`	Follows import aliases to the original
`getFullyQualifiedName(symbol)`	Dotted symbol path

Type queries:

Method	Description
`getTypeAtLocation(node)`	Inferred/declared type at a node
`getTypeOfSymbolAtLocation(sym, node)`	Type of a symbol at a specific usage
`getContextualType(expr)`	Expected type from surrounding context
`getBaseTypes(type)`	Base types of a class or interface
`getUnionType(types)`	Construct a union type
`isAssignableTo(source, target)`	Assignability check

Signature queries:

Method	Description
`getSignaturesOfType(type, kind)`	Call or construct signatures
`getReturnTypeOfSignature(sig)`	Return type of a `Signature`
`getTypePredicateOfSignature(sig)`	Type predicate, if any
`getParametersOfSignature(sig)`	Parameter symbols

Display utilities:

Method	Description
`typeToString(type, enclosingDeclaration?, flags?)`	Human-readable type string
`symbolToString(symbol, enclosingDeclaration?, meaning?, flags?)`	Human-readable symbol name
`signatureToString(sig, enclosingDeclaration?, flags?, kind?)`	Signature display string

Sources: src/compiler/checker.ts1-1155 tests/baselines/reference/api/typescript.d.ts3000-3200

`Symbol` and `Type` Interfaces

`Symbol`

interface Symbol {
    flags: SymbolFlags;
    escapedName: __String;
    declarations?: Declaration[];
    valueDeclaration?: Declaration;
    members?: SymbolTable;
    exports?: SymbolTable;
    getName(): string;
    getFlags(): SymbolFlags;
    getDeclarations(): Declaration[] | undefined;
    getDocumentationComment(checker): SymbolDisplayPart[];
    getJsDocTags(checker?): JSDocTagInfo[];
}

SymbolFlags is a bitflag enum indicating what kind of thing a symbol represents (e.g., Function, Class, Interface, Variable, TypeAlias, Module, etc.).

Sources: src/services/services.ts656-796 src/compiler/types.ts4000-4100

`Type`

Type is the base interface for all TypeScript types. Concrete kinds are distinguished by TypeFlags:

`TypeFlags` member	Meaning
`String`, `Number`, `Boolean`	Primitive types
`StringLiteral`, `NumberLiteral`	Literal types
`Object`	Object type (class, interface, type literal)
`Union`	Union type (`A \| B`)
`Intersection`	Intersection type (`A & B`)
`TypeParameter`	Generic type parameter
`Conditional`	Conditional type
`TemplateLiteral`	Template literal type
`Any`, `Unknown`, `Never`, `Void`	Special types

Subtypes like UnionType, IntersectionType, ObjectType, and InterfaceType carry additional data. ObjectType uses ObjectFlags to distinguish classes, interfaces, tuples, mapped types, etc.

Sources: src/compiler/types.ts5000-5200 tests/baselines/reference/api/typescript.d.ts1600-1900

`NodeBuilderFlags` and Type Display

When converting a Type or Symbol back to an AST node (e.g., for generating .d.ts output or display), the TypeChecker accepts NodeBuilderFlags to control the output:

Flag	Effect
`NoTruncation`	Disable type truncation
`WriteArrayAsGenericType`	Use `Array<T>` instead of `T[]`
`UseStructuralFallback`	Fall back to structural type notation
`OmitParameterModifiers`	Strip access modifiers from parameters
`UseFullyQualifiedType`	Always fully-qualify type names

Sources: src/compiler/types.ts4800-4900 tests/baselines/reference/api/typescript.d.ts1400-1500

Important Utility Functions

These are exported directly from the ts namespace and commonly used by API consumers:

Function	Description
`forEachChild(node, cb, cbArray?)`	Iterate the immediate children of a node
`getPositionOfLineAndCharacter(sf, line, character)`	Line/col to offset
`getLineAndCharacterOfPosition(sf, position)`	Offset to line/col
`isIdentifier(node)`	Node type guard
`isFunctionDeclaration(node)`	Node type guard
`isClassDeclaration(node)`	Node type guard
`flattenDiagnosticMessageText(msg, newLine)`	Flatten `DiagnosticMessageChain` to string
`getDefaultLibFilePath(options)`	Path to appropriate `lib.d.ts`
`parseCommandLine(commandLine, readFile?)`	Parse CLI-style args
`readConfigFile(fileName, readFile)`	Read a `tsconfig.json`
`parseJsonConfigFileContent(...)`	Parse the content of a tsconfig
`findConfigFile(searchPath, fileExists, configName?)`	Walk up directories to find tsconfig
`version`	The TypeScript compiler version string

Sources: src/compiler/utilities.ts1-620 src/compiler/program.ts328-340 tests/baselines/reference/api/typescript.d.ts3430-3550

`CompilerOptions` Key Properties

CompilerOptions mirrors the properties of tsconfig.json's compilerOptions. Commonly used fields:

Field	Type	tsconfig equivalent
`target`	`ScriptTarget`	`"target"`
`module`	`ModuleKind`	`"module"`
`moduleResolution`	`ModuleResolutionKind`	`"moduleResolution"`
`strict`	`boolean`	`"strict"`
`outDir`	`string`	`"outDir"`
`declaration`	`boolean`	`"declaration"`
`sourceMap`	`boolean`	`"sourceMap"`
`jsx`	`JsxEmit`	`"jsx"`
`lib`	`string[]`	`"lib"`
`noEmit`	`boolean`	`"noEmit"`

Sources: src/compiler/commandLineParser.ts1-130 src/compiler/types.ts6000-6200

`EmitResult` and `Diagnostic`

program.emit() returns an EmitResult:

interface EmitResult {
    emitSkipped: boolean;
    diagnostics: readonly Diagnostic[];
    emittedFiles?: string[];
}

Diagnostic is the common error/warning representation:

interface Diagnostic extends DiagnosticRelatedInformation {
    category: DiagnosticCategory;   // Error, Warning, Message, Suggestion
    code: number;                   // numeric error code
    file: SourceFile | undefined;
    start: number | undefined;
    length: number | undefined;
    messageText: string | DiagnosticMessageChain;
}

DiagnosticCategory has values: Warning = 0, Error = 1, Suggestion = 2, Message = 3.

Sources: src/compiler/types.ts1700-1800 tests/baselines/reference/api/typescript.d.ts2000-2100

API Surface Stability

The public API boundary is enforced by baseline testing. The file tests/baselines/reference/api/typescript.d.ts is generated from the compiled output and checked into the repository. Any PR that changes the public API surface causes this baseline to differ, which fails CI and requires an explicit baseline update. This prevents accidental public API changes.

All internal-only symbols are annotated /** @internal */ in the source. These do not appear in the public baseline and should not be relied upon by external consumers.

Sources: tests/baselines/reference/api/typescript.d.ts1-20 src/compiler/types.ts782-848

Relationship to Other Systems

For the Language Service (completions, refactors, etc.) built on top of these APIs, see Language Service.
For tsserver and its JSON protocol (how editors communicate with TypeScript), see Language Server.
For incremental builds and BuilderProgram, see Incremental and Project Builds.
For the standard library declaration files referenced via getDefaultLibFilePath, see Standard Library.

Sources: src/services/services.ts1-360 src/server/session.ts1-100 src/compiler/program.ts1-326

Public Compiler API

Relevant source files

Overview

The API has three main uses:

Use Case	Primary Entry Points
Full compilation (type-check + emit)	`createProgram`, `Program.emit`
Single-file parsing only	`createSourceFile`
Single-file transpilation (no type-check)	`transpileModule`
Editor / tooling integration	`createLanguageService`

High-Level Component Map

The diagram below maps user-facing API calls to the internal compiler components they drive.

Diagram: Public API Entry Points to Internal Components

Sources: src/compiler/program.ts328-340 src/services/services.ts1-360 tests/baselines/reference/api/typescript.d.ts1-50

Entry Point: `createProgram`

createProgram is the primary entry point for full compilations. It accepts either a list of root file names and options, or a CreateProgramOptions object.

createProgram(rootNames, options, host?, oldProgram?, configFileParsingDiagnostics?)
createProgram(options: CreateProgramOptions)

The returned Program object is the top-level handle for all subsequent operations. Its key methods are:

Method	Description
`getSourceFiles()`	Returns all `SourceFile` nodes in the program
`getSourceFile(fileName)`	Looks up a specific `SourceFile`
`getTypeChecker()`	Returns the `TypeChecker` for semantic queries
`emit(targetSourceFile?, writeFile?, ...)`	Runs the emitter; returns `EmitResult`
`getSyntacticDiagnostics(sourceFile?)`	Parse-level errors
`getSemanticDiagnostics(sourceFile?)`	Type-level errors
`getDeclarationDiagnostics(sourceFile?)`	Errors from `.d.ts` generation
`getCompilerOptions()`	Returns the active `CompilerOptions`
`getRootFileNames()`	Returns the initial root file list
`getResolvedModuleFromModuleSpecifier(...)`	Module resolution result

Sources: src/compiler/program.ts1-326 tests/baselines/reference/api/typescript.d.ts3200-3350

Entry Point: `createSourceFile`

createSourceFile(
    fileName: string,
    sourceText: string,
    languageVersionOrOptions: ScriptTarget | CreateSourceFileOptions,
    setParentNodes?: boolean,
    scriptKind?: ScriptKind
): SourceFile

Parses a single source text string into a SourceFile AST node without creating a full Program. Useful for tooling that only needs the parse tree.

setParentNodes — if true, sets the parent pointer on every AST node (required for many utilities)
scriptKind — controls parsing mode: TS, TSX, JS, JSX, JSON, etc.

Sources: src/compiler/parser.ts1-440 tests/baselines/reference/api/typescript.d.ts3380-3400

Entry Point: `transpileModule`

transpileModule(input: string, transpileOptions: TranspileOptions): TranspileOutput

TranspileOutput contains:

outputText — the emitted JavaScript string
sourceMapText — optional source map JSON string
diagnostics — any syntactic errors encountered

Sources: tests/baselines/reference/api/typescript.d.ts3400-3430

Entry Point: `createLanguageService`

createLanguageService(
    host: LanguageServiceHost,
    documentRegistry?: DocumentRegistry,
    syntaxOnlyOrLanguageServiceMode?: boolean | LanguageServiceMode
): LanguageService

Sources: src/services/services.ts1-360 src/services/types.ts1-100

`CompilerHost` Interface

CompilerHost is the file system and environment abstraction used by createProgram. Callers can supply a custom host to redirect file I/O (e.g. for in-memory compilation or virtual file systems).

Key required methods:

Method	Description
`fileExists(fileName)`	Check if a file exists
`readFile(fileName)`	Read file contents as a string
`getSourceFile(fileName, languageVersion, ...)`	Parse and return a `SourceFile`
`getDefaultLibFileName(options)`	Path to the default library (`lib.d.ts`)
`writeFile(fileName, data, ...)`	Write output files
`getCurrentDirectory()`	Current working directory
`getCanonicalFileName(fileName)`	Normalize file name casing
`useCaseSensitiveFileNames()`	Whether file names are case-sensitive
`getNewLine()`	Line ending string

A default host for Node.js is available via createCompilerHost(options).

Sources: src/compiler/types.ts5500-5600 tests/baselines/reference/api/typescript.d.ts3300-3380

The `Program` Object and Compilation Flow

Diagram: Program Lifecycle and Internal Calls

Sources: src/compiler/program.ts1-326 src/compiler/binder.ts1-310 src/compiler/checker.ts1-1155 src/compiler/emitter.ts1-430

AST Representation

`SourceFile`

A SourceFile is the root AST node for a single file. Key properties:

Property	Type	Description
`fileName`	`string`	Absolute file path
`text`	`string`	Full source text
`statements`	`NodeArray<Statement>`	Top-level statements
`languageVersion`	`ScriptTarget`	Target script version
`scriptKind`	`ScriptKind`	JS/TS/JSX variant
`isDeclarationFile`	`boolean`	Whether this is a `.d.ts` file
`referencedFiles`	`FileReference[]`	Triple-slash references
`diagnostics`	(internal)	Parse errors

`Node`

Method	Description
`getSourceFile()`	Enclosing `SourceFile`
`getStart(sf?, includeJsDoc?)`	Start position (skipping trivia)
`getFullStart()`	Start position including leading trivia
`getEnd()`	End position
`getText(sf?)`	Source text substring
`getChildren(sf?)`	Child nodes including trivia tokens
`forEachChild(cb, cbArray?)`	Iterate direct children

`SyntaxKind` Enum

SyntaxKind is a large const enum (src/compiler/types.ts40-492) that assigns an integer to every possible node and token kind. Key ranges:

Range	Description
`Unknown` .. `EndOfFileToken`	Special/trivial tokens
`NumericLiteral` .. `NoSubstitutionTemplateLiteral`	Literal tokens
`OpenBraceToken` .. `CaretEqualsToken`	Punctuation and operators
`BreakKeyword` .. `DeferKeyword`	Keywords
`QualifiedName` .. `ImportType`	Type nodes
`SourceFile`	Source file root
`FirstJSDocNode` .. `LastJSDocNode`	JSDoc nodes

Sources: src/compiler/types.ts40-492 src/services/services.ts374-495

Semantic Model: `TypeChecker`

The TypeChecker is obtained from program.getTypeChecker(). It provides all semantic analysis queries. It is lazy — most analysis only occurs when a method is called.

Diagram: TypeChecker Key Methods and What They Return

`TypeChecker` Method Groups

Symbol queries:

Method	Description
`getSymbolAtLocation(node)`	Symbol for an identifier or declaration
`getSymbolsInScope(location, meaning)`	All symbols visible at a position
`getExportsOfModule(symbol)`	Exported symbols of a module
`getPropertiesOfType(type)`	Property symbols of an object type
`getAliasedSymbol(symbol)`	Follows import aliases to the original
`getFullyQualifiedName(symbol)`	Dotted symbol path

Type queries:

Method	Description
`getTypeAtLocation(node)`	Inferred/declared type at a node
`getTypeOfSymbolAtLocation(sym, node)`	Type of a symbol at a specific usage
`getContextualType(expr)`	Expected type from surrounding context
`getBaseTypes(type)`	Base types of a class or interface
`getUnionType(types)`	Construct a union type
`isAssignableTo(source, target)`	Assignability check

Signature queries:

Method	Description
`getSignaturesOfType(type, kind)`	Call or construct signatures
`getReturnTypeOfSignature(sig)`	Return type of a `Signature`
`getTypePredicateOfSignature(sig)`	Type predicate, if any
`getParametersOfSignature(sig)`	Parameter symbols

Display utilities:

Method	Description
`typeToString(type, enclosingDeclaration?, flags?)`	Human-readable type string
`symbolToString(symbol, enclosingDeclaration?, meaning?, flags?)`	Human-readable symbol name
`signatureToString(sig, enclosingDeclaration?, flags?, kind?)`	Signature display string

Sources: src/compiler/checker.ts1-1155 tests/baselines/reference/api/typescript.d.ts3000-3200

`Symbol` and `Type` Interfaces

`Symbol`

interface Symbol {
    flags: SymbolFlags;
    escapedName: __String;
    declarations?: Declaration[];
    valueDeclaration?: Declaration;
    members?: SymbolTable;
    exports?: SymbolTable;
    getName(): string;
    getFlags(): SymbolFlags;
    getDeclarations(): Declaration[] | undefined;
    getDocumentationComment(checker): SymbolDisplayPart[];
    getJsDocTags(checker?): JSDocTagInfo[];
}

SymbolFlags is a bitflag enum indicating what kind of thing a symbol represents (e.g., Function, Class, Interface, Variable, TypeAlias, Module, etc.).

Sources: src/services/services.ts656-796 src/compiler/types.ts4000-4100

`Type`

Type is the base interface for all TypeScript types. Concrete kinds are distinguished by TypeFlags:

`TypeFlags` member	Meaning
`String`, `Number`, `Boolean`	Primitive types
`StringLiteral`, `NumberLiteral`	Literal types
`Object`	Object type (class, interface, type literal)
`Union`	Union type (`A \| B`)
`Intersection`	Intersection type (`A & B`)
`TypeParameter`	Generic type parameter
`Conditional`	Conditional type
`TemplateLiteral`	Template literal type
`Any`, `Unknown`, `Never`, `Void`	Special types

Subtypes like UnionType, IntersectionType, ObjectType, and InterfaceType carry additional data. ObjectType uses ObjectFlags to distinguish classes, interfaces, tuples, mapped types, etc.

Sources: src/compiler/types.ts5000-5200 tests/baselines/reference/api/typescript.d.ts1600-1900

`NodeBuilderFlags` and Type Display

When converting a Type or Symbol back to an AST node (e.g., for generating .d.ts output or display), the TypeChecker accepts NodeBuilderFlags to control the output:

Flag	Effect
`NoTruncation`	Disable type truncation
`WriteArrayAsGenericType`	Use `Array<T>` instead of `T[]`
`UseStructuralFallback`	Fall back to structural type notation
`OmitParameterModifiers`	Strip access modifiers from parameters
`UseFullyQualifiedType`	Always fully-qualify type names

Sources: src/compiler/types.ts4800-4900 tests/baselines/reference/api/typescript.d.ts1400-1500

Important Utility Functions

These are exported directly from the ts namespace and commonly used by API consumers:

Function	Description
`forEachChild(node, cb, cbArray?)`	Iterate the immediate children of a node
`getPositionOfLineAndCharacter(sf, line, character)`	Line/col to offset
`getLineAndCharacterOfPosition(sf, position)`	Offset to line/col
`isIdentifier(node)`	Node type guard
`isFunctionDeclaration(node)`	Node type guard
`isClassDeclaration(node)`	Node type guard
`flattenDiagnosticMessageText(msg, newLine)`	Flatten `DiagnosticMessageChain` to string
`getDefaultLibFilePath(options)`	Path to appropriate `lib.d.ts`
`parseCommandLine(commandLine, readFile?)`	Parse CLI-style args
`readConfigFile(fileName, readFile)`	Read a `tsconfig.json`
`parseJsonConfigFileContent(...)`	Parse the content of a tsconfig
`findConfigFile(searchPath, fileExists, configName?)`	Walk up directories to find tsconfig
`version`	The TypeScript compiler version string

Sources: src/compiler/utilities.ts1-620 src/compiler/program.ts328-340 tests/baselines/reference/api/typescript.d.ts3430-3550

`CompilerOptions` Key Properties

CompilerOptions mirrors the properties of tsconfig.json's compilerOptions. Commonly used fields:

Field	Type	tsconfig equivalent
`target`	`ScriptTarget`	`"target"`
`module`	`ModuleKind`	`"module"`
`moduleResolution`	`ModuleResolutionKind`	`"moduleResolution"`
`strict`	`boolean`	`"strict"`
`outDir`	`string`	`"outDir"`
`declaration`	`boolean`	`"declaration"`
`sourceMap`	`boolean`	`"sourceMap"`
`jsx`	`JsxEmit`	`"jsx"`
`lib`	`string[]`	`"lib"`
`noEmit`	`boolean`	`"noEmit"`

Sources: src/compiler/commandLineParser.ts1-130 src/compiler/types.ts6000-6200

`EmitResult` and `Diagnostic`

program.emit() returns an EmitResult:

interface EmitResult {
    emitSkipped: boolean;
    diagnostics: readonly Diagnostic[];
    emittedFiles?: string[];
}

Diagnostic is the common error/warning representation:

interface Diagnostic extends DiagnosticRelatedInformation {
    category: DiagnosticCategory;   // Error, Warning, Message, Suggestion
    code: number;                   // numeric error code
    file: SourceFile | undefined;
    start: number | undefined;
    length: number | undefined;
    messageText: string | DiagnosticMessageChain;
}

DiagnosticCategory has values: Warning = 0, Error = 1, Suggestion = 2, Message = 3.

Sources: src/compiler/types.ts1700-1800 tests/baselines/reference/api/typescript.d.ts2000-2100

API Surface Stability

All internal-only symbols are annotated /** @internal */ in the source. These do not appear in the public baseline and should not be relied upon by external consumers.

Sources: tests/baselines/reference/api/typescript.d.ts1-20 src/compiler/types.ts782-848

Relationship to Other Systems

For the Language Service (completions, refactors, etc.) built on top of these APIs, see Language Service.
For tsserver and its JSON protocol (how editors communicate with TypeScript), see Language Server.
For incremental builds and BuilderProgram, see Incremental and Project Builds.
For the standard library declaration files referenced via getDefaultLibFilePath, see Standard Library.

Sources: src/services/services.ts1-360 src/server/session.ts1-100 src/compiler/program.ts1-326

Public Compiler API

Overview

High-Level Component Map

Entry Point: createProgram

Entry Point: createSourceFile

Entry Point: transpileModule

Entry Point: createLanguageService

CompilerHost Interface

The Program Object and Compilation Flow

AST Representation

SourceFile

Node

SyntaxKind Enum

Semantic Model: TypeChecker

TypeChecker Method Groups

Symbol and Type Interfaces

Symbol

Type

NodeBuilderFlags and Type Display

Important Utility Functions

CompilerOptions Key Properties

EmitResult and Diagnostic

API Surface Stability

Relationship to Other Systems

On this page

Public Compiler API

Overview

High-Level Component Map

Entry Point: createProgram

Entry Point: createSourceFile

Entry Point: transpileModule

Entry Point: createLanguageService

CompilerHost Interface

The Program Object and Compilation Flow

AST Representation

SourceFile

Node

SyntaxKind Enum

Semantic Model: TypeChecker

TypeChecker Method Groups

Symbol and Type Interfaces

Symbol

Type

NodeBuilderFlags and Type Display

Important Utility Functions

CompilerOptions Key Properties

EmitResult and Diagnostic

API Surface Stability

Relationship to Other Systems

On this page

Entry Point: `createProgram`

Entry Point: `createSourceFile`

Entry Point: `transpileModule`

Entry Point: `createLanguageService`

`CompilerHost` Interface

The `Program` Object and Compilation Flow

`SourceFile`

`Node`

`SyntaxKind` Enum

Semantic Model: `TypeChecker`

`TypeChecker` Method Groups

`Symbol` and `Type` Interfaces

`Symbol`

`Type`

`NodeBuilderFlags` and Type Display

`CompilerOptions` Key Properties

`EmitResult` and `Diagnostic`

Entry Point: `createProgram`

Entry Point: `createSourceFile`

Entry Point: `transpileModule`

Entry Point: `createLanguageService`

`CompilerHost` Interface

The `Program` Object and Compilation Flow

`SourceFile`

`Node`

`SyntaxKind` Enum

Semantic Model: `TypeChecker`

`TypeChecker` Method Groups

`Symbol` and `Type` Interfaces

`Symbol`

`Type`

`NodeBuilderFlags` and Type Display

`CompilerOptions` Key Properties

`EmitResult` and `Diagnostic`