microsoft/playwright · error · Error

Expected string for options.form["${name}"], found File. Ple

Error message

Expected string for options.form["${name}"], found File. Please use options.multipart instead.

What it means

Error "Expected string for options.form["${name}"], found File. Please use options.multipart instead." thrown in microsoft/playwright.

Source

Thrown at packages/playwright-core/src/client/fetch.ts:219

      if (options.data !== undefined) {
        if (isString(options.data)) {
          if (isJsonContentType(headers))
            jsonData = isJsonParsable(options.data) ? options.data : JSON.stringify(options.data);
          else
            postDataBuffer = Buffer.from(options.data, 'utf8');
        } else if (Buffer.isBuffer(options.data)) {
          postDataBuffer = options.data;
        } else if (typeof options.data === 'object' || typeof options.data === 'number' || typeof options.data === 'boolean') {
          jsonData = JSON.stringify(options.data);
        } else {
          throw new Error(`Unexpected 'data' type`);
        }
      } else if (options.form) {
        if (globalThis.FormData && options.form instanceof FormData) {
          formData = [];
          for (const [name, value] of options.form.entries()) {
            if (typeof value !== 'string')
              throw new Error(`Expected string for options.form["${name}"], found File. Please use options.multipart instead.`);
            formData.push({ name, value });
          }
        } else {
          formData = objectToArray(options.form);
        }
      } else if (options.multipart) {
        multipartData = [];
        if (globalThis.FormData && options.multipart instanceof FormData) {
          const form = options.multipart;
          for (const [name, value] of form.entries()) {
            if (isString(value)) {
              multipartData.push({ name, value });
            } else {
              const file: ServerFilePayload = {
                name: value.name,
                mimeType: value.type,
                buffer: Buffer.from(await value.arrayBuffer()),
              };

View on GitHub (pinned to c8fc3bf8d3)

When it happens

Trigger: Thrown at packages/playwright-core/src/client/fetch.ts:219 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/playwright@c8fc3bf8d3 (2026-08-12). Data as JSON: /api/errors/e32fad4e4695a65c. Report an issue: GitHub.