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Hou - Engineer & Tech Educator

Learn Modern JavaScript - Functions

JavaScript, beginner, tutorial, learn-modern-javascript1 min read


By the end of this tutorial, you will be able to:

  • use the ES6 arrow function syntax
  • create default function parameters

ES6 Functions: Arrow Functions

Arrow functions were introduced in ES6 and provide a simpler syntax for creating functions along with more intuitive handling of this.

Take a look at this example, which uses an ES5 function expression syntax:

1var printName = function (firstName, lastName) {
2 return `${firstName} ${lastName}`;

To convert the printName() function to use the ES6 arrow syntax, you will have to follow two steps:

  1. Drop the function keyword
  2. Add a fat arrow between the parentheses and opening curly brace

The resulting function will look like this:

1const printName = (firstName, lastName) => {
2 return `${firstName} ${lastName}`;

If your function immediately returns a value, the curly braces wrapping the function body and return statements are not needed and the value is implicitly returned. Here's the shorthand you can use:

1const printName = (firstName, lastName) => `${firstName} ${lastName}`;

Default Parameters

JavaScript function parameters default to undefined. If you want to set a different default value, you can specify default parameters when you define your function. Default parameters allow named parameters of a function to be initialized with default values if no value or undefined is passed during function invocation. For example,

1function add(a, b = 1) {
2 return a + b;
5console.log(multiply(5, 2)); // 7
7console.log(multiply(5)); // 6

Another example,

1function greeting(name = "Jane", greeting) {
2 return `${greeting}, ${name}! `;
5console.log(greeting("John", "Good morning"));
7console.log(greeting(undefined, "Good afternoon"));

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