Sanitizing user input in Vue - Step-by-Step Execution

Concept Flow - Sanitizing user input

User types input

↓

Input captured by Vue ref

↓

Sanitize input (remove unsafe chars)

↓

Update reactive state with clean input

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Display sanitized input in UI

User input is captured, cleaned to remove unsafe characters, then stored reactively and shown safely in the UI.

Execution Sample

Vue

import { ref } from 'vue'
const userInput = ref('')
function sanitize(input) {
  return input.replace(/[<>"'&]/g, '')
}
function onInput(event) {
  userInput.value = sanitize(event.target.value)
}

This Vue code captures user input, removes unsafe characters, and updates the reactive variable.

Execution Table

Step	User Input	Sanitize Function Output	Reactive State (userInput.value)	UI Display
1	<script>	script	script	script
2	Hello & welcome	Hello welcome	Hello welcome	Hello welcome
3	Use 'quotes'	Use quotes	Use quotes	Use quotes
4	5 > 3	5 3	5 3	5 3
5	Normal text	Normal text	Normal text	Normal text

💡 Input processed and sanitized for safe display in UI.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5
userInput.value	""	"script"	"Hello welcome"	"Use quotes"	"5 3"	"Normal text"

Key Moments - 2 Insights

Why do some characters disappear from the input after typing?

Because the sanitize function removes unsafe characters like <, >, &, and quotes to keep the input safe, as shown in execution_table rows 1-4.

Is the original user input stored anywhere?

No, only the sanitized version is stored in userInput.value, so unsafe characters are never saved or displayed, as seen in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution table, what is userInput.value after step 2?

A "Hello welcome"

B "Hello & welcome"

C "Hello welcome"

D "Hello &amp; welcome"

💡 Hint

Check the 'Reactive State (userInput.value)' column in row 2 of execution_table.

At which step does the sanitize function remove the single quotes?

A Step 1

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Sanitize Function Output' column for step 3 in execution_table.

If the sanitize function did not remove < and >, what would happen in the UI display?

A Unsafe HTML could be rendered, causing security risks

B Input would appear exactly the same

C Input would be empty

D Vue would throw an error

💡 Hint

Sanitizing removes unsafe characters to prevent HTML injection, as shown in concept_flow.

Concept Snapshot

Sanitizing user input in Vue:
- Capture input with ref and event handler
- Use a function to remove unsafe chars (e.g., <, >, &, quotes)
- Update reactive state with clean input
- Display sanitized input safely in UI
- Prevents security risks like HTML injection

Full Transcript

This visual trace shows how Vue captures user input, sanitizes it by removing unsafe characters such as <, >, &, and quotes, then updates the reactive variable userInput.value. The sanitized input is displayed safely in the UI, preventing security risks. Each step shows the input before and after sanitizing, how the reactive state changes, and what the user sees. Key moments clarify why characters disappear and why only sanitized input is stored. The quiz tests understanding of these changes and their importance.