Key Concepts

Review core concepts you need to learn to master this subject

Functions

Calling Functions

Function Parameters

return Keyword

Function Declaration

Anonymous Functions

Function Expressions

Arrow Functions (ES6)

Functions

// Defining the function:
function sum(num1, num2) {
  return num1 + num2;
}

// Calling the function:
sum(3, 6); // 9

Functions are one of the fundamental building blocks in JavaScript. A function is a reusable set of statements to perform a task or calculate a value. Functions can be passed one or more values and can return a value at the end of their execution. In order to use a function, you must define it somewhere in the scope where you wish to call it.

The example code provided contains a function that takes in 2 values and returns the sum of those numbers.

Functions
Lesson 1 of 1
  1. 1
    What are Functions?
    When first learning how to calculate the area of a rectangle, there’s a sequence of steps to calculate the correct answer: 1. Measure the width of the rectangle. 2. Measure the height of the rec…
    Start
  2. 2
    Function Declarations
    In JavaScript, there are many ways to create a function. One way to create a function is by using a function declaration. Just like how a variable declaration binds a value to a variable name, a …
    Start
  3. 3
    Calling a Function
    As we saw in previous exercises, a function declaration binds a function to an identifier. However, a function declaration does not ask the code inside the function body to run, it just declares …
    Start
  4. 4
    Parameters and Arguments
    So far, the functions we’ve created execute a task without an input. However, some functions can take inputs and use the inputs to perform a task. When declaring a function, we can specify its _par…
    Start
  5. 5
    Default Parameters
    One of the features added in ES6 is the ability to use default parameters. Default parameters allow parameters to have a predetermined value in case there is no argument passed into the function …
    Start
  6. 6
    Return
    When a function is called, the computer will run through the function’s code and evaluate the result of calling the function. By default that resulting value is undefined. function rectangleArea(…
    Start
  7. 7
    Helper Functions
    We can also use the return value of a function inside another function. These functions being called within another function are often referred to as helper functions. Since each function is carr…
    Start
  8. 8
    Function Expressions
    Another way to define a function is to use a function expression. To define a function inside an expression, we can use the function keyword. In a function expression, the function name is usuall…
    Start
  9. 9
    Arrow Functions
    ES6 introduced arrow function syntax, a shorter way to write functions by using the special “fat arrow” () => notation. Arrow functions remove the need to type out the keyword function every t…
    Start
  10. 10
    Concise Body Arrow Functions
    JavaScript also provides several ways to refactor arrow function syntax. The most condensed form of the function is known as concise body. We’ll explore a few of these techniques below: 1. Funct…
    Start
  11. 11
    Review Functions
    Give yourself a pat on the back, you just navigated through functions! In this lesson, we covered some important concepts about functions: * A function is a reusable block of code that group…
    Start

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