microsoft/TypeScript · error · Error

Unknown marker "${markerName}" Available markers: ${this.get

Error message

Unknown marker "${markerName}" Available markers: ${this.getMarkerNames().map(m => '"' + m + '"').join(", ")}

What it means

Thrown by getMarkerByName when the requested marker name is not present in testData.markerPositions. The message lists all available marker names (quoted, comma-separated) to help the author pick a valid one. Markers are declared in fourslash content with /*<markerName>*/ or object-marker syntax.

Source

Thrown at src/harness/fourslashImpl.ts:4475

                availableNames.push(fn);
            }
        });
        return { file, availableNames };
    }

    private hasFile(name: string): boolean {
        return this.tryFindFileWorker(name).file !== undefined;
    }

    private getLineColStringAtPosition(position: number, file: FourSlashFile = this.activeFile) {
        const pos = this.languageServiceAdapterHost.positionToLineAndCharacter(file.fileName, position);
        return `line ${(pos.line + 1)}, col ${pos.character}`;
    }

    public getMarkerByName(markerName: string): Marker {
        const markerPos = this.testData.markerPositions.get(markerName);
        if (markerPos === undefined) {
            throw new Error(`Unknown marker "${markerName}" Available markers: ${this.getMarkerNames().map(m => '"' + m + '"').join(", ")}`);
        }
        else {
            return markerPos;
        }
    }

    public setCancelled(numberOfCalls: number): void {
        this.cancellationToken.setCancelled(numberOfCalls);
    }

    public resetCancelled(): void {
        this.cancellationToken.resetCancelled();
    }

    public getEditsForFileRename({ oldPath, newPath, newFileContents, preferences }: FourSlashInterface.GetEditsForFileRenameOptions): void {
        const test = (fileContents: { readonly [fileName: string]: string; }, description: string): void => {
            const changes = this.languageService.getEditsForFileRename(oldPath, newPath, this.formatCodeSettings, preferences);
            this.testNewFileContents(changes, fileContents, description);

View on GitHub (pinned to b465fdbfe1)

Solutions

Compare the requested name against the available markers listed in the error message.
Add the missing marker at the intended position using /*<myMarker>*/ in the test content.
Fix the typo or use the correct existing marker name.

Example fix

// before — content has /*<start>*/ but test says
// goTo.marker("begin");
// after
goTo.marker("start");

Defensive patterns

Strategy: validation

Validate before calling

function assertMarkerExists(state: FourSlashTestState, name: string) {
    if (!state.getMarkerNames().includes(name)) {
        throw new Error(`Marker '${name}' missing. Known: ${state.getMarkerNames().join(", ")}`);
    }
}

Prevention

Declare each marker with /*<name>*/ at the exact caret target before referencing it.
Keep marker names short and unique to avoid duplicates that confuse lookups.

When it happens

Trigger: Calling goTo.marker("myMarker") / getMarkerByName("myMarker") in a fourslash test that has no marker with that name. getMarkerNames() reflects only markers defined via the fourslash marker syntax during parseFileContent.

Common situations: Typo in the marker name, marker was removed during an edit, or the marker syntax is malformed so it was never registered. Also happens when copying a test that referenced markers without copying the marker definitions.

Related errors

AI-assisted analysis of microsoft/TypeScript@b465fdbfe1 (2026-08-12). Data as JSON: /api/errors/1697364fe8be9a6b. Report an issue: GitHub.