Using the Compiler API

##Disclaimer Keep in mind that this is not yet a stable API - we’re releasing this as version 0.4, and things will be changing over time. As a first iteration, there will be a few rough edges. We encourage any and all feedback from the community to improve the API. To allow users to transition between future releases, we will be documenting any breaking changes to this API per new release.

Getting set up

First you'll need to install TypeScript >=1.5 from npm.

For API Samples compatible with TypeScript == 1.4 please see Using the Compiler API (TypeScript 1.4)

Once that's done, you'll need to link it from wherever your project resides. If you don't link from within a Node project, it will just link globally.

npm install -g typescript
npm link typescript

Once that's done, just grab our definitions file either

• By using tsd with the command tsd query typescript --action install.
• Going directly to the source on our repository.

For a overview of the general TypeScript compiler architecture and layering, see Architectural Overview

That's it, you're ready to go. Now you can try out some of the following examples.

A minimal compiler

Let's try to write a barebones compiler that can compile a TypeScript string to its corresponding JavaScript. We will need to create a Program. This is as simple as calling createProgram. createProgram abstracts any interaction with the underlying system in the CompilerHost interface. The CompilerHost allows the compiler to read and write files, get the current directory, ensure that files and directories exist, and query some of the underlying system properties such as case sensitivity and new line characters. For convenience, we expose a function to create a default host using createCompilerHost.

/// <reference path="typings/node/node.d.ts" />
/// <reference path="typings/typescript/typescript.d.ts" />

import ts = require("typescript");

export function compile(fileNames: string[], options: ts.CompilerOptions): void {
    var program = ts.createProgram(fileNames, options);
    var emitResult = program.emit();

    var allDiagnostics = ts.getPreEmitDiagnostics(program).concat(emitResult.diagnostics);

    allDiagnostics.forEach(diagnostic => {
        var { line, character } = diagnostic.file.getLineAndCharacterOfPosition(diagnostic.start);
        var message = ts.flattenDiagnosticMessageText(diagnostic.messageText, '\n');
        console.log(`${diagnostic.file.fileName} (${line + 1},${character + 1}): ${message}`);
    });

    var exitCode = emitResult.emitSkipped ? 1 : 0;
    console.log(`Process exiting with code '${exitCode}'.`);
    process.exit(exitCode);
}

compile(process.argv.slice(2), {
    noEmitOnError: true, noImplicitAny: true,
    target: ts.ScriptTarget.ES5, module: ts.ModuleKind.CommonJS
});

A simple transform function

Creating a compiler is simple enough, but you may want to just get the corresponding JavaScript output given TypeScript sources. For this you can use ts.transpile to get a string => string transformation in two lines.

/// <reference path="typings/typescript/typescript.d.ts" />

import * as ts from "typescript";

const source = "let x: string  = 'string'";

let result = ts.transpile(source, { module: ts.ModuleKind.CommonJS });

console.log(JSON.stringify(result));

Traversing the AST with a little linter

As mentioned above, the Node interface is the root of our AST. Generally, we use the forEachChild function in a recursive manner to traverse. This subsumes the visitor pattern and often gives more flexibility.

As an example of how one could traverse the AST, consider a minimal linter that does the following:

• Checks that all looping construct bodies are enclosed by curly braces.
• Checks that all if/else bodies are enclosed by curly braces.
• The "stricter" equality operators (===/!==) are used instead of the "loose" ones (==/!=).

/// <reference path="typings/node/node.d.ts" />
/// <reference path="typings/typescript/typescript.d.ts" />

import {readFileSync} from "fs";
import * as ts from "typescript";

export function delint(sourceFile: ts.SourceFile) {
    delintNode(sourceFile);

    function delintNode(node: ts.Node) {
        switch (node.kind) {
            case ts.SyntaxKind.ForStatement:
            case ts.SyntaxKind.ForInStatement:
            case ts.SyntaxKind.WhileStatement:
            case ts.SyntaxKind.DoStatement:
                if ((<ts.IterationStatement>node).statement.kind !== ts.SyntaxKind.Block) {
                    report(node, "A looping statement's contents should be wrapped in a block body.");
                }
                break;

            case ts.SyntaxKind.IfStatement:
                let ifStatement = (<ts.IfStatement>node);
                if (ifStatement.thenStatement.kind !== ts.SyntaxKind.Block) {
                    report(ifStatement.thenStatement, "An if statement's contents should be wrapped in a block body.");
                }
                if (ifStatement.elseStatement &&
                    ifStatement.elseStatement.kind !== ts.SyntaxKind.Block &&
                    ifStatement.elseStatement.kind !== ts.SyntaxKind.IfStatement) {
                    report(ifStatement.elseStatement, "An else statement's contents should be wrapped in a block body.");
                }
                break;

            case ts.SyntaxKind.BinaryExpression:
                let op = (<ts.BinaryExpression>node).operatorToken.kind;
                if (op === ts.SyntaxKind.EqualsEqualsToken || op == ts.SyntaxKind.ExclamationEqualsToken) {
                    report(node, "Use '===' and '!=='.")
                }
                break;
        }

        ts.forEachChild(node, delintNode);
    }

    function report(node: ts.Node, message: string) {
        let { line, character } = sourceFile.getLineAndCharacterOfPosition(node.getStart());
        console.log(`${sourceFile.fileName} (${line + 1},${character + 1}): ${message}`);
    }
}

const fileNames = process.argv.slice(2);
fileNames.forEach(fileName => {
    // Parse a file
    let sourceFile = ts.createSourceFile(fileName, readFileSync(fileName).toString(), ts.ScriptTarget.ES6, /*setParentNodes */ true);

    // delint it
    delint(sourceFile);
});

In this example, we did not need to create a type checker because all we wanted to do was traverse each SourceFile.

Incremental build support using the language services

Please refer to the Using the Language Service API page for more details.

The services layer provide a set of additional set of utilities that can help simplify some complex scenarios. In the snippet below, we will try to build an incremental build server that watches a set of files and update the only the outputs of the file that changed. We will achieve this through creating a LanguageService object. Similar to the program in the previous example, we need a LanguageServiceHost. The LanguageServiceHost augments the concept of a file with a version, isOpen flag, and a ScriptSnapshot. Version, allows the language service to track changes to files. isOpen, tells the language service to keep AST in memory as the file is in use. ScriptSnapshot is an abstraction over text that allows the language service to query for changes.

/// <reference path="typings/node/node.d.ts" />
/// <reference path="typings/typescript/typescript.d.ts" />

import * as fs from "fs";
import * as ts from "typescript";

function watch(rootFileNames: string[], options: ts.CompilerOptions) {
    const files: ts.Map<{ version: number }> = {};

    // initialize the list of files
    rootFileNames.forEach(fileName => {
        files[fileName] = { version: 0 };
    });

    // Create the language service host to allow the LS to communicate with the host
    const servicesHost: ts.LanguageServiceHost = {
        getScriptFileNames: () => rootFileNames,
        getScriptVersion: (fileName) => files[fileName] && files[fileName].version.toString(),
        getScriptSnapshot: (fileName) => {
            if (!fs.existsSync(fileName)) {
                return undefined;
            }

            return ts.ScriptSnapshot.fromString(fs.readFileSync(fileName).toString());
        },
        getCurrentDirectory: () => process.cwd(),
        getCompilationSettings: () => options,
        getDefaultLibFileName: (options) => ts.getDefaultLibFilePath(options),
    };

    // Create the language service files
    const services = ts.createLanguageService(servicesHost, ts.createDocumentRegistry())

    // Now let's watch the files
    rootFileNames.forEach(fileName => {
        // First time around, emit all files
        emitFile(fileName);

        // Add a watch on the file to handle next change
        fs.watchFile(fileName,
            { persistent: true, interval: 250 },
            (curr, prev) => {
                // Check timestamp
                if (+curr.mtime <= +prev.mtime) {
                    return;
                }

                // Update the version to signal a change in the file
                files[fileName].version++;

                // write the changes to disk
                emitFile(fileName);
            });
    });

    function emitFile(fileName: string) {
        let output = services.getEmitOutput(fileName);

        if (!output.emitSkipped) {
            console.log(`Emitting ${fileName}`);
        }
        else {
            console.log(`Emitting ${fileName} failed`);
            logErrors(fileName);
        }

        output.outputFiles.forEach(o => {
            fs.writeFileSync(o.name, o.text, "utf8");
        });
    }

    function logErrors(fileName: string) {
        let allDiagnostics = services.getCompilerOptionsDiagnostics()
            .concat(services.getSyntacticDiagnostics(fileName))
            .concat(services.getSemanticDiagnostics(fileName));

        allDiagnostics.forEach(diagnostic => {
            let message = ts.flattenDiagnosticMessageText(diagnostic.messageText, "\n");
            if (diagnostic.file) {
                let { line, character } = diagnostic.file.getLineAndCharacterOfPosition(diagnostic.start);
                console.log(`  Error ${diagnostic.file.fileName} (${line + 1},${character + 1}): ${message}`);
            }
            else {
                console.log(`  Error: ${message}`);
            }
        });
    }
}

// Initialize files constituting the program as all .ts files in the current directory
const currentDirectoryFiles = fs.readdirSync(process.cwd()).
    filter(fileName=> fileName.length >= 3 && fileName.substr(fileName.length - 3, 3) === ".ts");

// Start the watcher
watch(currentDirectoryFiles, { module: ts.ModuleKind.CommonJS });

Pretty printer using the LS Formatter

The formatting interfaces used here are part of the typescript 1.4 package but is not currently exposed in the public typescript.d.ts. The typings should be exposed in the next release.

/// <reference path="typings/node/node.d.ts" />
/// <reference path="typings/typescript/typescript.d.ts" />

import ts = require("typescript");

// Note: this uses ts.formatting which is part of the typescript 1.4 package but is not currently 
//       exposed in the public typescript.d.ts. The typings should be exposed in the next release. 
function format(text: string) {
    var options = getDefaultOptions();

    // Parse the source text
    var sourceFile = ts.createSourceFile("file.ts", text, ts.ScriptTarget.Latest, "0");
    fixupParentReferences(sourceFile);

    // Get the formatting edits on the input sources
    var edits = (<any>ts).formatting.formatDocument(sourceFile, getRuleProvider(options), options);

    // Apply the edits on the input code
    return applyEdits(text, edits);

    function getRuleProvider(options: ts.FormatCodeOptions) {
        // Share this between multiple formatters using the same options.
        // This represents the bulk of the space the formatter uses.
        var ruleProvider = new (<any>ts).formatting.RulesProvider();
        ruleProvider.ensureUpToDate(options);
        return ruleProvider;
    }

    function applyEdits(text: string, edits: ts.TextChange[]): string {
        // Apply edits in reverse on the existing text
        var result = text;
        for (var i = edits.length - 1; i >= 0; i--) {
            var change = edits[i];
            var head = result.slice(0, change.span.start());
            var tail = result.slice(change.span.start() + change.span.length())
            result = head + change.newText + tail;
        }
        return result;
    }

    function getDefaultOptions(): ts.FormatCodeOptions {
        return {
            IndentSize: 4,
            TabSize: 4,
            NewLineCharacter: '\r\n',
            ConvertTabsToSpaces: true,
            InsertSpaceAfterCommaDelimiter: true,
            InsertSpaceAfterSemicolonInForStatements: true,
            InsertSpaceBeforeAndAfterBinaryOperators: true,
            InsertSpaceAfterKeywordsInControlFlowStatements: true,
            InsertSpaceAfterFunctionKeywordForAnonymousFunctions: false,
            InsertSpaceAfterOpeningAndBeforeClosingNonemptyParenthesis: false,
            PlaceOpenBraceOnNewLineForFunctions: false,
            PlaceOpenBraceOnNewLineForControlBlocks: false,
        };
    }

    function fixupParentReferences(sourceFile: ts.SourceFile) {
        var parent: ts.Node = sourceFile;
        function walk(n: ts.Node): void {
            n.parent = parent;

            var saveParent = parent;
            parent = n;
            ts.forEachChild(n, walk);
            parent = saveParent;
        }
        ts.forEachChild(sourceFile, walk);
    }
}


var code = "var a=function(v:number){return 0+1+2+3;\n}";
var result = format(code);
console.log(result);