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Form Guards

Most of the guards here are file checkers, which should have been in separate file-guards page/section, they are here because they were used in FormData creation and validation.

isValidFormData​

Checks if a value is a valid non-empty FormData instance.

Function Signature​

function isValidFormData(value: unknown): value is FormData

Parameters​

  • value: The value to check

Returns​

true if:

  • Value is a FormData instance
  • Has entries (not empty)
  • Supports .entries() method

Example​

const formData = new FormData();
formData.append('name', 'John');

isValidFormData(formData); // true
isValidFormData({}); // false

SSR Note​

⚠️ May not work in SSR environments like Next.js Server Components

isOriginFileObj​

Checks if a value is an OriginFileObj (extended File with UID). For Ant-Design Upload component.

Function Signature​

function isOriginFileObj(value: unknown): value is OriginFileObj

Type Definition​

/** * Represents the original file object before any modifications. */
interface OriginFileObj extends File {
 /** Unique identifier for the original file. */
 uid: string;
}

Validation Rules​

  • Must be an object
  • Must have string uid property
  • Inherits all File properties

Example​

const file = new File([], 'test.txt');
const originFile = Object.assign(file, { uid: '123' });

isOriginFileObj(originFile); // true
isOriginFileObj(file); // false

isCustomFile​

Checks if a value is a CustomFile object.

Function Signature​

function isCustomFile(value: unknown): value is CustomFile

Type Definition​

/** * Represents a custom file structure used in file upload components. */
interface CustomFile {
 /** Unique identifier for the file. */
 uid: string;
 /** The timestamp (milliseconds) when the file was last modified. */
 lastModified: number;
 /** A string representation of the last modified date. */
 lastModifiedDate: Date;
 /** The name of the file. */
 name: string;
 /** The size of the file in bytes. */
 size: number;
 /** The MIME type of the file. */
 type: string;
 /** Upload progress percentage (0-100). */
 percent: number;
 /** The original file object before any transformations. */
 originFileObj: OriginFileObj;
 /** The URL for a thumbnail preview of the file. */
 thumbUrl: string;
 /** Optional error information if the upload fails. */
 error?: FileError;
 /** Optional server response after a successful upload. */
 response?: string;
 /** Optional status of the file upload (e.g., "uploading", "done", "error"). */
 status?: string;
}

/** * Represents an error that occurs during a file upload. */
interface FileError extends Error {
 /** HTTP status code of the error. */
 status: number;
 /** The HTTP method used for the request (e.g., "POST", "PUT"). */
 method: string;
 /** The URL where the upload was attempted. */
 url: string;
}

Validation Rules​

  • Must be an object
  • Must have originFileObj property that passes isOriginFileObj
  • Contains all required CustomFile properties

Example​

const customFile = {
  uid: '123',
  name: 'file.txt',
  originFileObj: originFile, // from previous example
  // ...other required properties
};

isCustomFile(customFile); // true

isCustomFileArray​

Checks if a value is an array of CustomFile objects.

Function Signature​

function isCustomFileArray(value: unknown): value is CustomFile[]

Validation Rules​

  • Must be non-empty array
  • Every element must pass isCustomFile

Example​

const files = [customFile1, customFile2]; 
isCustomFileArray(files); // true

isFileArray​

Checks if a value is an array of native File objects.

Function Signature​

function isFileArray(value: unknown): value is File[] | Blob[]

Validation Rules​

  • Must be non-empty array
  • Every element must be File instance

Example​

const files = [new File([], 'test.txt')];
isFileArray(files); // true

isFileList​

Checks if a value is a FileList instance.

Function Signature​

function isFileList(value: unknown): value is FileList

Validation Rules​

  • Must be FileList instance
  • Available in browser environments

Example​

const fileInput = document.querySelector('input[type="file"]');
isFileList(fileInput.files); // true

isFileOrBlob​

Checks if a given value is an instance of File or Blob.

Function Signature​

function isFileOrBlob(value: unknown): value is File | Blob

Validation Rules​

  • Must be File/Blob instance
  • Available in browser environments

Example​

const file = new File(['hello world'], 'hello.txt', {
 type: 'text/plain',
});
isFileOrBlob(file); // true

isFileUpload​

Checks if a value is a FileUpload object.

Function Signature​

function isFileUpload(value: unknown): value is FileUpload

Type Definition​

/** * Represents a file upload operation, commonly used in libraries like `FilePond` or `Ant Design Upload`. */
interface FileUpload {
 /** The primary file being uploaded. */
 file: File | CustomFile;
 /** The list of files associated with the upload. */
 fileList: CustomFile[];
}

Validation Rules​

  • Must be an object
  • Must have either:
    • file property that is File or CustomFile
    • fileList property that is CustomFile[]

Example​

const upload = {
  file: customFile,
  fileList: [customFile1, customFile2]
};
isFileUpload(upload); // true