How to check if you have written ES6 code?

To verify if you have used ES6 (ECMAScript 2015) features, consider the following points:

1. Using let and const instead of var: ES6 introduced let and const for variable declaration to resolve the scoping issues of var and provide block-level scoping. For example, demonstrate how to use let in loops to ensure loop variables are confined to the loop body.

   javascript
   for (let i = 0; i < 10; i++) {
       console.log(i); // i is only valid within this loop
   }
   ``
   

2. Arrow Functions: ES6 introduced arrow functions, which not only make code more concise but also resolve common issues with the this keyword. Show an example of using arrow functions for handling events or array operations.

   javascript
   const numbers = [1, 2, 3, 4];
   const squares = numbers.map(n => n * n);
   console.log(squares); // Output: [1, 4, 9, 16]
   ``
   

3. Template Literals: ES6 provides template literals to simplify string concatenation and support interpolation. Demonstrate how to use template literals to construct dynamic strings.

   javascript
   const name = "World";
   console.log(`Hello, ${name}!`); // Output: Hello, World!
   ``
   

4. Destructuring Assignment: ES6's destructuring assignment simplifies extracting data from arrays or objects. Show how to quickly extract and use properties from objects.

   javascript
   const person = { name: 'Alice', age: 25 };
   const { name, age } = person;
   console.log(name, age); // Output: Alice 25
   ``
   

5. Promises and Asynchronous Programming: ES6 introduced Promises, improving the experience of asynchronous programming. Provide an example of using Promises to handle asynchronous requests.

   javascript
   function fetchData(url) {
       return new Promise((resolve, reject) => {
           fetch(url)
               .then(response => response.json())
               .then(data => resolve(data))
               .catch(error => reject(error));
       });
   }
   ``
   

6. Modular Programming: ES6 promoted modular programming in JavaScript, supporting import and export syntax. Demonstrate how to import or export modules.

   javascript
   // file: math.js
   export const add = (a, b) => a + b;
   
   // file: app.js
   import { add } from './math';
   console.log(add(2, 3)); // Output: 5
   ``

Each of these points can serve as an indicator of whether ES6 features are being used. Assess this based on the presence of these features in your code. In interviews, showcasing your knowledge of ES6 features through concrete code examples effectively demonstrates your technical proficiency and adaptability to modern JavaScript development.