Creating a Function in JavaScript

We have seen examples of built-in functions in JavaScript:

• prompt() allows us to grab user inputted values to assign to a variable

• console.log() is a method from the console that outputs text to the console

Similar to how these features have a name, ability to take inputs, and work with the inputs. We can create our own functions in JavaScript.

Formatting a Custom Function in JavaScript

function name_of_function(parameter1, parameter2) {
    // Function's code goes in here.
}

• The keyword function is used to let JavaScript know that we are creating a function

• name_of_function is used to name our custom function

• (parameter1, parameter2) is used to define any required inputs. They act as placeholders for the values that will be given to the function since the program cannot be certain of what the values will be.

Example: A greeting function

// Custom Functions Defined
function greet() {
    console.log("Hello, I am a program!");
}
// End of Custom Functions

// Start of our code
console.log("Welcome to our program!");
greet();

Output:

"Welcome to our program!"
"Hello, I am a program!"

• Keyword function: This keyword is used to declare a function.

• Function Name greet: This is the name of the function. You can call this function using this name.

• Parentheses (): These are used to define parameters for the function. In this case, there are no parameters.

• Curly Braces {}: These define the body of the function, which contains the code that will be executed when the function is called.

• console.log: This is a method of the console object that outputs a message to the web console.

• String "Hello, I am a program!": This is the message that will be logged to the console.

• When a function is defined, it is not executed until the function is called upon

• The main instructions for the program starts under the comment: // Start of our code

  • The program will output first: "Welcome to our program!"

  • Then the program calls the function called greet()

  • The program then travels to the code block of greet() then executes the code to output "Hello, I am a program!"