GET requests in components in Vue - Step-by-Step Execution

Concept Flow - GET requests in components

Component starts

↓

Setup function runs

↓

Trigger GET request

↓

Fetch data from server

↓

Update reactive state

↓

Component re-renders with data

↓

User sees updated content

This flow shows how a Vue component triggers a GET request during setup, updates its state with the fetched data, and re-renders to show the new content.

Execution Sample

Vue

import { ref, onMounted } from 'vue';

export default {
  setup() {
    const data = ref(null);
    onMounted(async () => {
      const res = await fetch('https://api.example.com/data');
      data.value = await res.json();
    });
    return { data };
  }
};

This Vue component fetches data from an API when it mounts and stores it in a reactive variable to display.

Execution Table

Step	Action	State Before	State After	Output/Effect
1	Component setup starts	data = null	data = null	Component prepares reactive state
2	onMounted hook registered	data = null	data = null	Ready to fetch after mount
3	Component mounts	data = null	data = null	Trigger onMounted callback
4	Fetch GET request sent	data = null	data = null	Waiting for server response
5	Response received	data = null	data = {json data}	Data stored in reactive variable
6	Component re-renders	data = {json data}	data = {json data}	UI updates to show fetched data
7	User sees updated content	data = {json data}	data = {json data}	Data displayed on screen

💡 Data fetched and reactive state updated, component finished rendering with new data.

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
data	null	null	{json data}	{json data}

Key Moments - 3 Insights

Why does the data variable start as null and then change?

The data variable is initially null because no data is loaded yet. After the GET request completes (see step 5 in execution_table), the data variable updates with the fetched JSON, triggering the component to re-render.

Why do we use onMounted to trigger the GET request?

Using onMounted ensures the GET request runs only after the component is fully loaded in the browser, preventing errors and ensuring the UI is ready to update with the fetched data (see step 3 and 4).

What happens if the GET request takes time to respond?

The component shows no data (null) until the response arrives. Once the data is received (step 5), the reactive state updates and the UI refreshes automatically.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'data' after step 3?

A null

B {json data}

C undefined

D empty string

💡 Hint

Check the 'State After' column for step 3 in the execution_table.

At which step does the component update its UI with the fetched data?

A Step 4

B Step 6

C Step 5

D Step 7

💡 Hint

Look for the step where 'Component re-renders' and UI updates happen in the execution_table.

If the GET request URL changes, which step in the execution_table would be directly affected?

A Step 6

B Step 2

C Step 4

D Step 7

💡 Hint

Step 4 is when the fetch GET request is sent; changing the URL affects this step.

Concept Snapshot

Vue GET requests in components:
- Use onMounted() to run code after component loads
- Use fetch() with await to get data
- Store data in a reactive ref variable
- Updating ref triggers component re-render
- Display data reactively in template

Full Transcript

This visual trace shows how a Vue component performs a GET request. When the component starts, it sets a reactive variable 'data' to null. The onMounted hook waits until the component is fully loaded, then sends a fetch GET request to the server. While waiting, 'data' remains null. When the response arrives, the JSON data is stored in 'data'. This update triggers Vue to re-render the component, showing the new data on screen. This process ensures data loads smoothly after the component is ready, and the UI updates automatically when data arrives.