If you don't know any JavaScript, this is a quick 5 minute course explaining most things you will need to understand.

If you need a more in depth explanation you can look up anything on developer.mozilla.org, everything except for the dom will apply to gjs.

Semicolons

Semicolons are optional, as there is automatic semicolon insertions

Logging, printing

// in gjs and other runtimes
console.log("hello");

// in gjs
print("hello");
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Variables

To define a variable use the let or const keyword

let someString = "some-string";
let someNumber = 69;
let someBool = true;

const array = ["string", 69, true];

const object = {
  key: "value",
  "key-word": "value",
};
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Flow control

if else

let i = 0;
if (i < 0) {
  print("its negative");
} else if (i > 0) {
  print("its more than 0");
} else {
  print("its 0");
}
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while loop

let i = 0;
while (i < 5) {
  print(i);
  i++;
}
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for loop

for (let i = 0; i < 5; i++) {
  print(i);
}
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for of loop

const array = [0, 1, 2, 3, 4];
for (const item of array) {
  print(item);
}
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Functions

There are multiple ways to define functions, with the function keyword or with fat arrow functions, also know as lambda functions in other languages

named function

function fn(param1, param2) {
  print(param1, param2);
}
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nameless function assigned to a const variable

const fn = function (param1, param2) {
  print(param1, param2);
};
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fat arrow function a.k.a lambda

const fn = (param1, param2) => {
  print(param1, param2);
};
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invoke all of them like any other function

fn("hi", "mom");
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default parameter value

function fn(param1, param2 = "hello") {
  print(param1, param2);
}

fn(); // undefined, hello
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Destructuring

arrays

const array = [1, 2, 3, 4, 5];
const [elem1, elem2, ...rest] = array;
print(elem1, elem2, rest); // 1, 2, [3, 4, 5]
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objects

const object = { one: 1, two: 2, three: 3, four: 4 };
const { one, two, ...rest } = object;
print(one, two, rest); // 1, 2, {three: 3, four: 4}
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useful in function definitions

function fn({ one, two }) {
  print(one, two);
}

fn({ one: "hello", two: "mom" }); // hello, mom
fn(); // throws error because undefined can't be destructed
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Modules

exporting

export default "hello";
export const string = "mom";
export function fn(...params) {
  print(...params);
}
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importing

import hi, { fn, string } from "./path-to-file.js";
fn(hi, string); // hello, mom
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String formatting

use backticks and ${}

const string = "mom";
const formatted = `hi ${string}`;
print(formatted); // hi mom
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