public/subjects/you-spin-me-round/README.md

You Spin Me Round

Functions

Functions in JS allows you to describe multiple instructions, in other words, it's a way to execute code inside your code !

That seems pretty complicated but it is the building block of your programs.

You already have been using a function as console.log is one ! You can easly spot them because we stick parens after their identifiers ().

For example, here's a function call:

//       ↙ identifier, like variables
console.log('Hello There !')
//          ↖ open paren + argument + close paren

Function name (identifier or property.key)

The first things that appears in a function is the identifier, in fact, in JS, functions are values of type function. This means that in order to be used a function must be either assigned to:

• a variable
• or an object property

Function calling

Functions do something, and they can return a result, a value.

console.log does not return a value, but it will do something: make its arguments appear in the console.

To call the function, in other word run it, we need too add ().

console.log // function is not used, nothing happen
console.log() // function was called ! an empty line appear in the console
console.log(4) // function was called with 4 and it appears in the console

Function arguments

So in that last example, number 4 was the argument of the console.log function.

A function will execute the same code on different arguments, making them flexible.

Sometimes, arguments are named parameters. We just like to use 10 different names for everything to sound "smart".

JS gives you plenty of readymade functions, for now we are going to focus on Math functions.

function return values

All functions from the JS Math object do nothing other than compute a new value from its argument.

For example, the well named Math.round function will take a number as argument and returns the rounded value of this number.

To use return values, assign them to variables:

let roundedValue = Math.round(1.8) // Here we assign the result of the function call
console.log(roundedValue) // 2

The variable roundedValue value is the number 2, the result of the function call.

Nested function calls

It is also possible to use the return value of a function directly without using an intermediary variable.
For example we could have written:

console.log(Math.round(3.2)) // double functions call !!!! woaaaa

Here we first call Math.round(3.2) which returns the number 3 and that will be passed to console.log that will procede to display it.

Instructions

We have prepared a variable num. Just as a warm up, use this variable num as argument of some Math functions.

• Declare a rounded variable of num rounded value.
• Declare a truncated variable of num truncated value.

One of the necessary Math function is already used in the lessons examples before the instructions. Explore the link below to see which others functions the Math object contains in order to find what you need to complete this exercise.

Notions

• Math