JAVASCRIPT

06: FUNCTIONS

What are functions and their headers, calls, parameters, and returns?

WHAT IS A FUNCTION

​

• Block of code designed to perform particular task
• Function is executed when the function is called
• Makes code more efficient and readable
• Can put code into a function and then call that function each time you need to run that code instead of simply repeating it

FUNCTION HEADER

function square(num) {

return num * num;

​

}

• Used to declare a new function
• First line of a function is the function header
• Used to declare a new function
• In the format function keyword, name, (parameters)

​

function name(parameter1, parameter2, parameter3) {

// code to be executed

}

Header

CALLING A FUNCTION

• Put the function keyword, function name, and parentheses
• Put the values you want to pass into the function between the parentheses (as parameters)
• Make sure the number of values you put in matches the number of parameters in the header

function toCelsius(fahrenheit) {

return (5/9) * (fahrenheit-32);

}

​

let value = toCelsius(77); // function calling

value = (5/9) * (77-32);

WHAT IS A PARAMETER

• Variable passed into a function
• Put the name of the parameter in between
• Type is not necessary for JavaScript
• Parameters are separated by commas
• Can put as many as you want
• Terminology:
• Parameters are listed inside the parentheses () in the function definition
• Function arguments are the actual values a function receives when it is called

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WHAT IS AN ARGUMENT

​

function toCelsius(fahrenheit) {

return (5/9) * (fahrenheit-32);

}

​

let value = toCelsius(77);

• A value passed to a function when the function is called
• Different from parameter
• Parameter is the variable
• Argument is the value
• Also called actual parameter

Parameter

Argument

FUNCTION RETURN

• Function will stop executing when the return statement is reached
• Return value can be “caught” with a variable or used like a variable

// Function is called, the return value will end up in x

let x = myFunction(4, 3);

​

function myFunction(a, b) {

// Function returns the product of a and b

return a * b;

}

TRY IT YOURSELF

Go to onecompiler.com/javascript

Create a function that concatenates strings, try calling it, and see what else you can do!

FUNCTIONS REVIEW

Go to gimkit.com/join

THANKS!

Any questions?

codingpower101@gmail.com

codingpower.org