Deleting files in Firebase - Time & Space Complexity

Time Complexity: Deleting files

O(n)

Understanding Time Complexity

When deleting files in Firebase Storage, it's important to know how the time needed grows as you delete more files.

We want to understand how the number of files affects the total time to delete them all.

Scenario Under Consideration

Analyze the time complexity of the following operation sequence.

import { getStorage, ref, deleteObject } from "firebase/storage";

const storage = getStorage();
const fileRefs = [fileRef1, fileRef2, fileRef3];

for (const fileRef of fileRefs) {
  await deleteObject(fileRef);
}
    

This code deletes each file one by one from Firebase Storage using their references.

Identify Repeating Operations

Identify the API calls, resource provisioning, data transfers that repeat.

• Primary operation: The deleteObject API call to remove a single file.
• How many times: Once for each file in the list.

How Execution Grows With Input

Each file requires one delete call, so the total calls grow directly with the number of files.

Input Size (n)	Approx. Api Calls/Operations
10	10 delete calls
100	100 delete calls
1000	1000 delete calls

Pattern observation: The number of delete calls increases one-to-one with the number of files.

Final Time Complexity

Time Complexity: O(n)

This means the time to delete files grows linearly with how many files you want to delete.

Common Mistake

[X] Wrong: "Deleting multiple files at once takes the same time as deleting one file."

[OK] Correct: Each file requires its own delete call, so more files mean more calls and more time.

Interview Connect

Understanding how operations scale helps you design efficient cloud processes and explain your reasoning clearly in interviews.

Self-Check

"What if we delete files in parallel instead of one by one? How would the time complexity change?"

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