CookieStorage.getItem() type definition should include undefined

[mikurikuri11]

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• I have searched for duplicate or closed issues
• I have read the guide for submitting bug reports
• I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue

Category

Authentication (amazon-cognito-identity-js)

Bug Description

The CookieStorage.getItem() method's type definition returns string, but the actual implementation returns string | undefined.

Current type definition (index.d.ts):

export class CookieStorage implements ICognitoStorage {
    getItem(key: string): string;  // ← Missing undefined
}

Actual implementation (CookieStorage.js):

getItem(key) {
    return Cookies.get(key);  // js-cookie returns undefined when key doesn't exist
}

The js-cookie library's `Cookies.get(key)` returns `undefined` when the key doesn't exist, not an empty string.

Expected Behavior

The type definition should match the actual runtime behavior:

export class CookieStorage implements ICognitoStorage {
    getItem(key: string): string | undefined;
}

Reproduction

import { CookieStorage } from 'amazon-cognito-identity-js';

const storage = new CookieStorage({ domain: 'example.com' });
const value = storage.getItem('non-existent-key');

// TypeScript thinks: value is string
// Runtime reality: value is undefined
console.log(typeof value);  // "undefined"
console.log(value === undefined);  // true

Code Snippet

// This code has a bug that TypeScript cannot catch:
const value = storage.getItem(key);
if (value !== '') {  // Developer expects empty string for missing key
    return value;    // undefined passes this check!
}

Package version

amazon-cognito-identity-js@6.x

Additional context

Note: The `ICognitoStorage` interface correctly defines `getItem(key: string): string | null`, but `CookieStorage` class overrides this with just `string`, which is both incorrect and misleading.

[osama-rizk]

Hi @mikurikuri11,

Thank you for creating this issue.

You're correct - the type definition should be string | undefined since js-cookie returns undefined for missing keys.

Have you considered upgrading to Amplify v6? The newer version has significantly improved TypeScript definitions and better type safety. You can find more information about the updated token storage mechanisms here.