Deleting files in Firebase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic method to delete a file in Firebase Storage?

Use the delete() method on a reference to the file you want to remove.

beginner

What happens if you try to delete a file that does not exist in Firebase Storage?

The delete() method will fail and return an error indicating the file was not found.

beginner

How do you get a reference to a file in Firebase Storage before deleting it?

Use firebase.storage().ref('path/to/file') to get the reference.

intermediate

Why is it important to handle errors when deleting files in Firebase Storage?

Because network issues or missing files can cause deletion to fail, and handling errors helps keep your app stable.

intermediate

Can you delete multiple files at once in Firebase Storage with a single command?

No, you must delete each file individually by calling delete() on each file's reference.

Which Firebase Storage method deletes a file?

A delete()

B remove()

C destroy()

D erase()

The correct method to delete a file in Firebase Storage is delete().

What do you need before calling delete() on a file?

A File content

B User authentication token

C A file reference

D File metadata

You must have a reference to the file in Firebase Storage before you can delete it.

If a file does not exist, what happens when you call delete()?

A It throws an error

B It silently succeeds

C It deletes a new empty file

D It creates a backup

Calling delete() on a non-existent file results in an error.

Can you delete multiple files with one delete() call?

A Only if files share the same name

B Yes, if files are in the same folder

C Yes, using a batch delete method

D No, you must delete each file separately

Firebase Storage requires deleting files one by one using their references.

Why should you handle errors when deleting files?

A To retry deletion automatically

B To keep the app stable and inform users

C To speed up deletion

D To backup files before deletion

Handling errors helps keep your app stable and lets you inform users if deletion fails.

Explain the steps to delete a file in Firebase Storage.

Think about how you find the file and what you do to remove it safely.

Why is error handling important when deleting files in Firebase Storage?

Consider what might go wrong during deletion and how your app should respond.

Practice

1. What does the deleteObject function do in Firebase Storage?

easy

A. It creates a new folder in Firebase Storage.

B. It uploads a new file to Firebase Storage.

C. It reads the contents of a file in Firebase Storage.

D. It deletes a file from Firebase Storage.

Solution

1. Step 1: Understand the purpose of deleteObject

   The deleteObject function is designed to remove files from Firebase Storage.

2. Step 2: Compare with other functions

   Uploading files uses uploadBytes, reading uses getDownloadURL, and folders are virtual, not created by deleteObject.

3. Final Answer:

   It deletes a file from Firebase Storage. -> Option D

4. Quick Check:

   deleteObject removes files = A [OK]

Hint: Remember: deleteObject means remove file [OK]

Common Mistakes:

• Confusing deleteObject with upload functions
• Thinking deleteObject creates folders
• Assuming deleteObject reads file content

2. Which of the following is the correct syntax to delete a file named image.png from Firebase Storage using JavaScript?

easy

A. storage.delete('image.png');

B. await deleteFile('image.png');

C. await deleteObject(ref(storage, 'image.png'));

D. deleteObject('image.png');

Solution

1. Step 1: Identify correct function and parameters

   The deleteObject function requires a reference to the file, created by ref(storage, 'filename').

2. Step 2: Check syntax correctness

   await deleteObject(ref(storage, 'image.png')); correctly uses await deleteObject(ref(storage, 'image.png'));. Other options use incorrect functions or missing references.

3. Final Answer:

   await deleteObject(ref(storage, 'image.png')); -> Option C

4. Quick Check:

   Use ref() with deleteObject = C [OK]

Hint: Use ref() to locate file before deleteObject [OK]

Common Mistakes:

• Calling deleteObject without ref()
• Using non-existent deleteFile function
• Omitting await for async deleteObject

3. Consider this code snippet:

const fileRef = ref(storage, 'docs/report.pdf');
try {
  await deleteObject(fileRef);
  console.log('File deleted');
} catch (error) {
  console.log('Error:', error.message);
}

What will be printed if the file docs/report.pdf does not exist?

medium

A. 'File deleted'

B. 'Error: File not found'

C. No output

D. SyntaxError

Solution

1. Step 1: Understand deleteObject behavior on missing file

   If the file does not exist, deleteObject throws an error caught by the catch block.

2. Step 2: Check catch block output

   The catch block logs the error message, which typically indicates the file was not found.

3. Final Answer:

   'Error: File not found' -> Option B

4. Quick Check:

   Missing file causes error message = B [OK]

Hint: Missing file triggers catch error message [OK]

Common Mistakes:

• Assuming deleteObject silently succeeds if file missing
• Expecting no output on error
• Confusing error message with syntax error

4. Identify the error in this code snippet that tries to delete a file:

const fileRef = ref('storage', 'photos/pic.jpg');
deleteObject(fileRef).then(() => {
  console.log('Deleted');
}).catch(error => {
  console.error(error);
});

medium

A. The ref function is called with wrong arguments.

B. deleteObject should not use promises.

C. Missing await keyword before deleteObject.

D. The file path should not include folders.

Solution

1. Step 1: Check ref function usage

   The ref function requires the storage instance as the first argument, not the string 'storage'.

2. Step 2: Validate other parts

   Using promises with then and catch is valid. Await is optional here. File paths can include folders.

3. Final Answer:

   The ref function is called with wrong arguments. -> Option A

4. Quick Check:

   ref() needs storage instance, not string = A [OK]

Hint: ref() needs storage object, not string 'storage' [OK]

Common Mistakes:

• Passing string 'storage' instead of storage object
• Thinking await is mandatory with promises
• Believing file paths cannot have folders

5. You want to delete multiple files in Firebase Storage: file1.txt, file2.txt, and file3.txt. Which approach correctly deletes all files and logs 'All deleted' only after all deletions succeed?

hard

A. Use Promise.all with deleteObject calls for each file reference.

B. Call deleteObject sequentially without waiting for promises.

C. Use a for loop with deleteObject but no await or Promise.all.

D. Delete only the first file; others delete automatically.

Solution

1. Step 1: Understand asynchronous deletion

   Each deleteObject returns a promise. To wait for all deletions, use Promise.all.

2. Step 2: Check other options

   Sequential calls without waiting may not complete before logging. For loop without await or Promise.all won't wait. Files do not delete automatically.

3. Final Answer:

   Use Promise.all with deleteObject calls for each file reference. -> Option A

4. Quick Check:

   Promise.all waits for all deletes = D [OK]

Hint: Use Promise.all to wait for multiple deletes [OK]

Common Mistakes:

• Not waiting for all delete promises
• Assuming deleting one file deletes others
• Ignoring asynchronous nature of deleteObject