Why input validation is critical in Express - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get user input from the request body in Express.

Express

app.post('/submit', (req, res) => {
  const userInput = req.body.[1];
  res.send('Received');
});

Drag options to blanks, or click blank then click option'

Avalue

Bdata

Cuser

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong key name that does not exist in req.body.

Trying to get input from req.params instead of req.body.

The user input is usually accessed from req.body using the key that matches the form field name, here 'input'.

2fill in blank

medium

Complete the code to check if the user input is empty and respond with an error.

Express

app.post('/submit', (req, res) => {
  const input = req.body.input;
  if (input [1] '') {
    return res.status(400).send('Input is required');
  }
  res.send('Input received');
});

Drag options to blanks, or click blank then click option'

A===

B!==

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of === which can cause unexpected results.

Checking for truthiness instead of empty string.

We check if the input is exactly equal to an empty string to detect missing input.

3fill in blank

hard

Fix the error in the input validation to ensure only numbers are accepted.

Express

app.post('/submit', (req, res) => {
  const input = req.body.input;
  if (!Number.isInteger([1])) {
    return res.status(400).send('Input must be an integer');
  }
  res.send('Valid input');
});

Drag options to blanks, or click blank then click option'

AparseInt(input)

BNumber(input)

Cinput

Dinput.length

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'input' directly without conversion, as it's a string.

Passing input.length which is a number but unrelated to input value.

Since req.body.input is typically a string, convert it to a number using Number(input) first. Then Number.isInteger() checks if it's an integer.

4fill in blank

hard

Fill both blanks to sanitize and validate user input as a trimmed non-empty string.

Express

app.post('/submit', (req, res) => {
  const input = req.body.input[1]();
  if (input [2] '') {
    return res.status(400).send('Input cannot be empty');
  }
  res.send('Input accepted');
});

Drag options to blanks, or click blank then click option'

Atrim

B===

C!==

DtoLowerCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using toLowerCase instead of trim which does not remove spaces.

Using !== instead of === which reverses the logic.

Using trim() removes spaces around the input. Then checking if it is exactly equal to empty string detects empty input after trimming.

5fill in blank

hard

Fill all three blanks to validate input length and type before processing.

Express

app.post('/submit', (req, res) => {
  const input = req.body.input;
  if (typeof input !== [1] || input.length [2] 0 || input.length [3] 100) {
    return res.status(400).send('Invalid input');
  }
  res.send('Input is valid');
});

Drag options to blanks, or click blank then click option'

A'string'

B>

C<=

D'number'

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for type 'number' instead of 'string'.

Using wrong comparison operators that invert the logic.

We check that input is a string, its length is greater than 0, and length is less than or equal to 100 to ensure valid input size.