In JavaScript, you can use the encodeURIComponent, encodeURI, decodeURIComponent, and decodeURI functions to encode or decode URLs or their components.

1. Encoding a URL

Use encodeURI or encodeURIComponent to encode URLs or parts of them.

• encodeURI: Encodes a full URL, leaving special characters like :, /, ?, &, and = intact.
• encodeURIComponent: Encodes individual components of a URL, including all special characters.

// Example of encodeURI
const url = "https://example.com/page?name=John Doe&age=30";
const encodedURL = encodeURI(url);
console.log(encodedURL); 
// Output: https://example.com/page?name=John%20Doe&age=30

// Example of encodeURIComponent
const queryParam = "John Doe";
const encodedParam = encodeURIComponent(queryParam);
console.log(encodedParam);
// Output: John%20Doe

2. Decoding a URL

Use decodeURI or decodeURIComponent to decode previously encoded URLs or components.

• decodeURI: Decodes a full URL that was encoded using encodeURI.
• decodeURIComponent: Decodes a URL component that was encoded using encodeURIComponent.

// Example of decodeURI
const encodedURL = "https://example.com/page?name=John%20Doe&age=30";
const decodedURL = decodeURI(encodedURL);
console.log(decodedURL); 
// Output: https://example.com/page?name=John Doe&age=30

// Example of decodeURIComponent
const encodedParam = "John%20Doe";
const decodedParam = decodeURIComponent(encodedParam);
console.log(decodedParam);
// Output: John Doe

3. Key Differences Between encodeURI and encodeURIComponent

Function	Use Case	Encodes Special Characters Like :, /, ?, &, =
encodeURI	Full URL (leaves URL syntax characters)	No
encodeURIComponent	URL components (encodes everything)	Yes

4. Example: Building a Query String

When constructing a query string for a URL, you can encode each parameter using encodeURIComponent:

const baseURL = "https://example.com/search";
const params = {
  query: "JavaScript tips",
  page: 2,
  sort: "relevance"
};

// Construct query string
const queryString = Object.keys(params)
  .map(key => `${encodeURIComponent(key)}=${encodeURIComponent(params[key])}`)
  .join("&");

const fullURL = `${baseURL}?${queryString}`;
console.log(fullURL);
// Output: https://example.com/search?query=JavaScript%20tips&page=2&sort=relevance