Diagnostics (compile errors) can be retrieved on the project or on source files:

const diagnostics = project.getPreEmitDiagnostics();

// or on a source file
const sourceFileDiagnostics = sourceFile.getPreEmitDiagnostics();

The pre-emit diagnostics are the syntactic, semantic, global, options, config file parsing, and if enabled the declaration diagnostics.

Formatting for Output

To nicely output the diagnostics, use project.formatDiagnosticsWithColorAndContext:

const diagnostics = project.getPreEmitDiagnostics();



Message text

Returned message text could be a string or a DiagnosticMessageChain:

const message = diagnostic.getMessageText();

Source file

Source file the diagnostic occurs in:

const sourceFile = diagnostic.getSourceFile(); // returns: SourceFile | undefined

Start, line number, & length

Position in the file, the line number, and length of the diagnostic:

const start = diagnostic.getStart(); // returns: number
const lineNumber = diagnostic.getLineNumber(); // returns: number
const length = diagnostic.getLength(); // returns: number


Categories can be warnings, errors, or just messages.

const category = diagnostic.getCategory(); // returns: DiagnosticCategory


This is the error code number:

const code = diagnostic.getCode(); // returns: number


todo: I don't know what this is, but it's available to get from the diagnostic.

const source = diagnostic.getSource(); // returns: string | undefined


A diagnostic message chain (DMC) will be returned by diagnostic.getMessageText() in certain scenarios.

According to the typescript compiler:

* A linked list of formatted diagnostic messages to be used as part of a multiline message.
* It is built from the bottom up, leaving the head to be the "main" diagnostic.
* While it seems that DiagnosticMessageChain is structurally similar to DiagnosticMessage,
* the difference is that messages are all preformatted in DMC.

The properties of a DMC are similar to a Diagnostic:

const messageText = dmc.getMessageText(); // returns: string
const category = dmc.getCategory(); // returns: DiagnosticCategory
const code = dmc.getCode(); // returns: number

Next DMC in linked list

Call .getNext():

const next = dmc.getNext(); // returns: DiagnosticMessageChain | undefined