## Key Concepts

Review core concepts you need to learn to master this subject

### Arrow Functions (ES6)

``````// Arrow function with two arguments
const sum = (firstParam, secondParam) => {
return firstParam + secondParam;
};
console.log(sum(2,5)); // Prints: 7

// Arrow function with no arguments
const printHello = () => {
console.log('hello');
};
printHello(); // Prints: hello

// Arrow functions with a single argument
const checkWeight = weight => {
console.log(`Baggage weight : \${weight} kilograms.`);
};
checkWeight(25); // Prints: Baggage weight : 25 kilograms.

// Concise arrow functions
const multiply = (a, b) => a * b;
console.log(multiply(2, 30)); // Prints: 60 ``````

Arrow function expressions were introduced in ES6. These expressions are clean and concise. The syntax for an arrow function expression does not require the `function` keyword and uses a fat arrow `=>` to separate the parameter(s) from the body.

There are several variations of arrow functions:

• Arrow functions with a single parameter do not require `()` around the parameter list.
• Arrow functions with a single expression can use the concise function body which returns the result of the expression without the `return` keyword.
Functions
Lesson 1 of 1
1. 1
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…
2. 2
In JavaScript, there are many ways to create a function. One way to create a function is by using a _function decl…
3. 3
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 …
4. 4
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…
5. 5
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 …
6. 6
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(…
7. 7
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…
8. 8
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…
9. 9
ES6 introduced arrow function syntax, a shorter way to write functions by using the special “fat arrow” () => notation. [Arrow functions](https://www.codecademy.com/resources/docs/javascript/ar…
10. 10
JavaScript also provides several ways to refactor arrow function syntax. The most condensed form of the func…
11. 11
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…

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