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Instructions for Logging Issues

1. Read the FAQ

Please read the FAQ before logging new issues, even if you think you have found a bug.

Issues that ask questions answered in the FAQ will be closed without elaboration.

2. Search for Duplicates

Search the existing issues before logging a new one.

Some search tips:

  • Don't restrict your search to only open issues. An issue with a title similar to yours may have been closed as a duplicate of one with a less-findable title.
  • Check for synonyms. For example, if your bug involves an interface, it likely also occurs with type aliases or classes.
  • Search for the title of the issue you're about to log. This sounds obvious but 80% of the time this is sufficient to find a duplicate when one exists.
  • Read more than the first page of results. Many bugs here use the same words so relevancy sorting is not particularly strong.
  • If you have a crash, search for the first few topmost function names shown in the call stack.

3. Do you have a question?

The issue tracker is for issues, in other words, bugs and suggestions. If you have a question, please use Stack Overflow, Gitter, your favorite search engine, or other resources. Due to increased traffic, we can no longer answer questions in the issue tracker.

4. Did you find a bug?

When logging a bug, please be sure to include the following:

  • What version of TypeScript you're using (run tsc --v)
  • If at all possible, an isolated way to reproduce the behavior
  • The behavior you expect to see, and the actual behavior

You can try out the nightly build of TypeScript (npm install typescript@next) to see if the bug has already been fixed.

5. Do you have a suggestion?

We also accept suggestions in the issue tracker. Be sure to check the FAQ and search first.

In general, things we find useful when reviewing suggestions are:

  • A description of the problem you're trying to solve
  • An overview of the suggested solution
  • Examples of how the suggestion would work in various places
    • Code examples showing e.g. "this would be an error, this wouldn't"
    • Code examples showing the generated JavaScript (if applicable)
  • If relevant, precedent in other languages can be useful for establishing context and expected behavior

Instructions for Contributing Code

Contributing bug fixes

TypeScript is currently accepting contributions in the form of bug fixes. A bug must have an issue tracking it in the issue tracker that has been approved ("Milestone == Community") by the TypeScript team. Your pull request should include a link to the bug that you are fixing. If you've submitted a PR for a bug, please post a comment in the bug to avoid duplication of effort.

Contributing features

Features (things that add new or improved functionality to TypeScript) may be accepted, but will need to first be approved (marked as "Milestone == Community" by a TypeScript coordinator with the message "Approved") in the suggestion issue. Features with language design impact, or that are adequately satisfied with external tools, will not be accepted.

Design changes will not be accepted at this time. If you have a design change proposal, please log a suggestion issue.


You will need to complete a Contributor License Agreement (CLA). Briefly, this agreement testifies that you are granting us permission to use the submitted change according to the terms of the project's license, and that the work being submitted is under appropriate copyright.

Please submit a Contributor License Agreement (CLA) before submitting a pull request. You may visit to sign digitally. Alternatively, download the agreement (Microsoft Contribution License Agreement.pdf), sign, scan, and email it back to Be sure to include your github user name along with the agreement. Once we have received the signed CLA, we'll review the request.


Your pull request should:

  • Include a description of what your change intends to do
  • Be a child commit of a reasonably recent commit in the master branch
    • Requests need not be a single commit, but should be a linear sequence of commits (i.e. no merge commits in your PR)
  • It is desirable, but not necessary, for the tests to pass at each commit
  • Have clear commit messages
    • e.g. "Refactor feature", "Fix issue", "Add tests for issue"
  • Include adequate tests
    • At least one test should fail in the absence of your non-test code changes. If your PR does not match this criteria, please specify why
    • Tests should include reasonable permutations of the target fix/change
    • Include baseline changes with your change
    • All changed code must have 100% code coverage
  • Follow the code conventions described in Coding guidelines
  • To avoid line ending issues, set autocrlf = input and whitespace = cr-at-eol in your git configuration

Contributing lib.d.ts fixes

The library sources are in: src/lib

Library files in built/local/ are updated by running


The files in lib/ are used to bootstrap compilation and usually do not need to be updated.

src/lib/dom.generated.d.ts and src/lib/webworker.generated.d.ts

These two files represent the DOM typings and are auto-generated. To make any modifications to them, please submit a PR to

Running the Tests

To run all tests, invoke the runtests-parallel target using jake:

jake runtests-parallel

This run will all tests; to run only a specific subset of tests, use:

jake runtests tests=<regex>

e.g. to run all compiler baseline tests:

jake runtests tests=compiler

or to run a specific test: tests\cases\compiler\2dArrays.ts

jake runtests tests=2dArrays

Debugging the tests

To debug the tests, invoke the runtests-browser task from jake. You will probably only want to debug one test at a time:

jake runtests-browser tests=2dArrays

You can specify which browser to use for debugging. Currently Chrome and IE are supported:

jake runtests-browser tests=2dArrays browser=chrome

You can debug with VS Code or Node instead with jake runtests debug=true:

jake runtests tests=2dArrays debug=true

Adding a Test

To add a new test case, simply place a .ts file in tests\cases\compiler containing code that exemplifies the bugfix or change you are making.

These files support metadata tags in the format // @metaDataName: value. The supported names and values are the same as those supported in the compiler itself, with the addition of the fileName flag. fileName tags delimit sections of a file to be used as separate compilation units. They are useful for tests relating to modules. See below for examples.

Note that if you have a test corresponding to a specific spec compliance item, you can place it in tests\cases\conformance in an appropriately-named subfolder. Note that filenames here must be distinct from all other compiler testcase names, so you may have to work a bit to find a unique name if it's something common.

Tests for multiple files

When one needs to test for scenarios which require multiple files, it is useful to use the fileName metadata tag as such:

// @fileName: file1.ts
export function f() {

// @fileName: file2.ts
import { f as g } from "file1";

var x = g();

One can also write a project test, but it is slightly more involved.

Managing the Baselines

Compiler testcases generate baselines that track the emitted .js, the errors produced by the compiler, and the type of each expression in the file. Additionally, some testcases opt in to baselining the source map output.

When a change in the baselines is detected, the test will fail. To inspect changes vs the expected baselines, use

jake diff

After verifying that the changes in the baselines are correct, run

jake baseline-accept

to establish the new baselines as the desired behavior. This will change the files in tests\baselines\reference, which should be included as part of your commit. It's important to carefully validate changes in the baselines.


All strings the user may see are stored in diagnosticMessages.json. If you make changes to it, run jake generate-diagnostics to push them to the Diagnostic interface in diagnosticInformationMap.generated.ts.

See coding guidelines on diagnostic messages.