JavaScript functions

The function

A function organizes a bunch of statements into more manageable chunks:

function doStuff(passedInVariable1, passedInVariable2, ...) {

    let task1 = passedInVariable1
    let task2 = passedInVariable2

    const addendum1 = 'and then go to sleep'
    const addendum2 = 'and then go to work'

    task1 += ' ' + addendum1
    task2 += ' ' + addendum2

    return task1 + ', then later: ' + task2

}

We can then call them again and again without having to re-write all the code in the function:

console.log(doStuff('eat dinner', 'eat breakfast'))
/* 
eat dinner and then go to sleep, 
then later: eat breakfast and go to work
*/

console.log(doStuff('take a bath', 'skip breakfast'))
/*
take a bath and then go to sleep, 
then later: skip breakfast and go to work
*/

So, functions provide a powerful mechanism for code re-use!

The return keyword

Inside the aforementioned function, doStuff , we see this return keyword which simply means this:

• When we make a call to doStuff , the call provides its return value

We can put a function call into a variable, in this case, with regime:

function doStuff(passedInVariable1, passedInVariable2, ...) {

    let task1 = passedInVariable1
    let task2 = passedInVariable2

    const addendum1 = 'and then go to sleep'
    const addendum2 = 'and then go to work'

    task1 += ' ' + addendum1
    task2 += ' ' + addendum2

    return task1 + ', then later: ' + task2

}

const regime = doStuff('eat dinner', 'eat breakfast')
console.log(regime)
/* 
eat dinner and then go to sleep, 
then later: eat breakfast and go to work
*/

When we use console.log on the variable regime, the console will output a version of the return statement, depending on the inputs!

A function does not need a return statement but it sure helps to have one :)

Function as an object

A newer way to write a function:

// ES6+ shorthand ("fat arrow notation")

const doStuff = (task1, task2) => {
    // function content
}

// or without shorthand

const doStuff2 = function(task1, task2) => {
    // function content
}

// or (older way)

const doStuff3 = function(task1, task2) {
    // function content
}

The "fat-arrow" (=>) notation differes from the older notation and we will discuss this in a future article!

Function as a property of an object

Methods are functions that are properties of an object:

const myObject = {
    someKey: "someValue",
    doStuff: function() {
        // function content - no declaration keyword required
    }
}

We will look objects in more detail in a future article!