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Polyfills & Transpilers

Code Quality: Polyfills & Transpilers

Describe what a JavaScript Transpiler does?​

View Answer:
Interview Response: A JavaScript transpiler converts source code written in one version or dialect of JavaScript into another, enabling modern features in older browsers or environments.

Code Example:

// before running the transpiler
height = height ?? 100;

// after running the transpiler
height = height !== undefined && height !== null ? height : 100;
note

Before 2020, JavaScript did not have a nullish coalescing operator (??). We needed a piece of software to convert it into workable code for older browsers to do work.

Why do developers use JavaScript transpilers?​

View Answer:
Interview Response: Developers use JavaScript transpilers to maintain compatibility across browsers, utilize modern language features, optimize code performance, and streamline development with modular, maintainable, and organized codebases.

What is Babel and how does it relate to JavaScript transpilers?​

View Answer:
Interview Response: Babel is a popular JavaScript transpiler that converts modern ES6+ syntax into ES5 code, enabling compatibility with older browsers and support for cutting-edge language features.

What is TypeScript, and how does it relate to JavaScript transpilers?​

View Answer:
Interview Response: TypeScript is a statically-typed superset of JavaScript that compiles to JavaScript, enhancing code maintainability, readability, and error detection with optional type annotations and transpilation.

Code Example:

JavaScript Code:

function greet(name) {
  return "Hello, " + name + "!";
}

const result = greet("John");
console.log(result);

TypeScript Code:

function greet(name: string): string {
  return `Hello, ${name}!`;
}

const result = greet("John");
console.log(result);

Can you name some other JavaScript transpilers besides Babel?​

View Answer:
Interview Response: Other JavaScript transpilers include Dart, Elm, Traceur, TypeScript, and CoffeeScript.

How do JavaScript transpilers impact website performance?​

View Answer:
Interview Response: JavaScript transpilers can impact website performance by generating optimized code, reducing file size through minification, and polyfilling features, but may introduce extra build-time complexity.

How do you configure a JavaScript transpiler?​

View Answer:
Interview Response: To configure a JavaScript transpiler, install it as a dependency, create a configuration file with required settings, and integrate it with your build process or development environment.

Code Example:

Here's an example of configuring Babel using a .babelrc file:

{
  "presets": ["@babel/preset-env"],
  "plugins": ["@babel/plugin-transform-arrow-functions"]
}

In this configuration, we specify that we want to use the @babel/preset-env preset, which enables transformation of JavaScript syntax based on target environments. We also include the @babel/plugin-transform-arrow-functions plugin, which transforms arrow functions to regular functions for broader browser compatibility.

Babel can be executed with this configuration file to transpile JavaScript code accordingly.

What is the difference between a transpiler and a compiler?​

View Answer:
Interview Response: A transpiler converts source code between similar languages or language versions, while a compiler translates high-level language code into low-level machine or assembly code for execution.

What is a Polyfill in JavaScript?​

View Answer:
Interview Response: A polyfill is a JavaScript code snippet that provides modern functionality in older browsers by emulating missing features, ensuring consistent behavior across different environments.

Code Example: Polyfill if Math.trunc function does not exist in an older engine.

if (!Math.trunc) {
  // if no such function
  // implement it
  Math.trunc = function (number) {
    // Math.ceil and Math.floor exist even in ancient JavaScript engines
    // they are covered later in the tutorial
    return number < 0 ? Math.ceil(number) : Math.floor(number);
  };
}

Why would you use a polyfill?​

View Answer:
Interview Response: We should use a polyfill to maintain cross-browser compatibility, ensuring consistent functionality and user experience when native support for specific features is lacking in older browsers.

How do you include a polyfill in your JavaScript code?​

View Answer:
Interview Response: To include a polyfill, either add the polyfill script directly in your HTML file or import it as a module in your JavaScript code, before using the desired feature.

How do you know which polyfill to use for a specific feature?​

View Answer:
Interview Response: To identify the right polyfill for a specific feature, consult compatibility tables on MDN Web Docs or caniuse.com to determine browser support. Review polyfill libraries, like core-js or polyfill.io, or search for reputable standalone polyfills. Check documentation, compatibility, and community feedback before selecting one.
View Answer:
Interview Response: Popular JavaScript polyfills include core-js, offering ECMAScript standard library polyfills, and polyfill.io, providing custom polyfill bundles based on the user's browser. These ensure consistent functionality across diverse browser environments.

Can polyfills negatively impact performance?​

View Answer:
Interview Response: Polyfills can negatively impact performance by increasing the JavaScript file size, potentially slowing down page load times, especially if multiple polyfills are used unnecessarily.

How can you optimize your use of polyfills to avoid performance issues?​

View Answer:
Interview Response: To optimize polyfill usage, only include necessary polyfills, use conditional loading to target specific browsers, bundle and minify polyfill files, and leverage CDNs for faster delivery.