JavaScript Functions

Question 1

What are Arrow Functions (ES6)?

Answer 1

Arrow function expressions were introduced in ES6. These expressions are clear 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.

Question 2

What are Functions?

Answer 2

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.

This example code contains a function that takes in two values and returns the sum of those numbers.
Example:
function sum (num1, num2) {
return num1 + num2;
}
// Calling the function:
sum (3, 6); // 9

Question 3

What are Function Parameters?

Answer 3

Inputs to functions are known as “parameters” when a function is declared or defined. Parameters are used as variables inside the function body. When the function is called, these parameters will have the value of whatever is “passed” in as “arguments”. It is possible to define a function without parameters.
Example:
// The parameter is name
function sayHello (name) {
return Hello, $(name}!;
}

Question 4

What does the “return” keyword mean?

Answer 4

Functions return (pass back) values using the “return” keyword. “return” ends function execution and returns the specified value to the location where it was called again. A common mistake is to forget the “return” keyword, in which case the function will return “undefined” by default.

Question 5

What is Function Declaration?

Answer 5

Function “declarations” are used to create named functions. These functions can be called using their declared name.

Question 6

How are Function Declarations built?

Answer 6

Function declarations are built from:
1. The “function” keyword
2. The function name
3. An optional list of parameters, separated by commas, enclosed by a set of parentheses ().
4. A function body enclosed in a set of curly braces {}.
Example:
function add (num1, num2) {
return num1 + num2;
}

Question 7

What does to Call a Function?

Answer 7

Functions can be “called”, or executed, elsewhere in code using parentheses following the function name. When a function is called, the code inside its function body runs.

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

// Calling the function
sum (2, 4); // 6

Question 8

What is an Argument?

Answer 8

“Arguments” are values passed into a function when it is called.