lesson_7_functions.md

Lesson 7 - Functions

Functions are a way to write reusable code and structure it usefully.

Functions look like this:

function functionName(argument1, argument2) {
    // Block of code that does something with the arguments
    return something // Optional: The function returns something, like a result from a calculation.
}

Function names

The name of the function should be as descriptive and concise as possible (similar to variable names).

Good names are: reverseArray, drawTriangle, login

Bad names are: h, reverseMethodTakingTwoParameters

Arguments

A function can have a number of arguments. An argument gets passed into the function when you call it and within the function, behaves like a variable.

Arguments are positional, so their order and position matters:

function multiplyArray(array, multiplyer) {
    // Implementation left as an excersise to the reader
}

multiplyArray([1,2,3,12], 12); // Works
multiplyArray(12, [1,2,3,4]); // Does not work

If you pass in variables into a function, the values¹ of the variables are now available as the arguments.

let array = [1,2,3];
let multiplyer = 3;

function multiplyArray(ar, mu) {
    let out = [];
    for(let i=0;i<ar.length, i++) {
        out[i] = ar[i] * mu;
    }
    return out;
}

multiplyArray(array, multiplyer); // Returns [3,6,9]
// array becomes ar in the function, multiplyer becomes mu in the function

Footnotes

1. That is not technically correct (If you really want to know, look up "pass by reference vs. pass by value") but it's good enough for now. ↩