Make Initialization Asynchronous in node.js - node.js

Question

I am trying to initialize a key class in a node.js program, but the instructions are running in arbitrary order and therefore it is initializing wrong. I've tried both making initialization happen in the definition and in a separate function; neither works. Is there something that I'm missing?
Current code:
class BotState {
constructor() {
this.bios = {}
this.aliases = {};
this.stories = {};
this.nextchar = 0;
}
}
var ProgramState = new BotState();
BotState.prototype.Initialize = function() {
this.bios = {};
var aliases = {};
var nextchar = 0;
this.nextchar = 0;
fs.readdir(biosdir, function (err, files) {
if (err) throw err;
for (var file in files) {
fs.readFile(biosdir + file + ".json", {flag: 'r'}, (err, data) => {
if (err) throw err;
var bio = JSON.parse(data);
var index = bio["charid"];
this.bios[index] = bio;
for (var alias in bio["aliaslist"]) {
this.aliases[bio["aliaslist"][alias].toLowerCase()] = index;
}
if (index >= nextchar) {
nextchar = index + 1;
}
})
}
this.stories = {};
this.nextchar = Math.max(Object.keys(aliases).map(key => aliases[key]))+1;
});
}
ProgramState.Initialize();
Is there some general way to make node.js just... run commands in the order they're written, as opposed to some arbitrary one?
(Apologies if the code is sloppy; I was more concerned with making it do the right thing than making it look nice.)

Answer 1

You are running an asynchronous operation in a loop which causes the loop to continue running and the asynchronous operations finish in some random order so you process them in some random order. The simplest way to control your loop is to switch to the promise-based version of the fs library and then use async/await to cause your for loop to pause and wait for the asynchronous operation to complete. You can do that like this:
const fsp = require('fs').promises;
class BotState {
constructor() {
this.bios = {}
this.aliases = {};
this.stories = {};
this.nextchar = 0;
}
}
var ProgramState = new BotState();
BotState.prototype.Initialize = async function() {
this.bios = {};
this.nextchar = 0;
let aliases = {};
let nextchar = 0;
const files = await fsp.readdir(biosdir);
for (const file of files) {
const data = await fsp.readFile(biosdir + file + ".json", {flag: 'r'});
const bio = JSON.parse(data);
const index = bio.charid;
const list = bio.aliaslist;
this.bios[index] = bio;
for (const alias of list) {
this.aliases[alias.toLowerCase()] = index;
}
if (index >= nextchar) {
nextchar = index + 1;
}
}
this.stories = {};
// there is something wrong with this line of code because you NEVER
// put any data in the variable aliases
this.nextchar = Math.max(Object.keys(aliases).map(key => aliases[key]))+1;
}
ProgramState.Initialize();
Note, there's a problem with your usage of the aliases local variable because you never put anything in that data structure, yet you're trying to use it in the last line of the function. I don't know what you're trying to accomplish there so you will have to fix that.
Also, note that you should never use for/in to iterate an array. That iterates properties of an object which can include more than just the array elements. for/of is made precisely for iterating an iterable like an array and it also saves the array dereference too as it gets you each value, not each index.