Variable throws initialization error after initializing it - javascript

I'm trying to make a Discord bot, one of its features is that it plays chess, at the start of the command, I read the JSON file, then check if it's undefined since I'll call a key from the object, so just in case it doesn't exist already, I'll create the data needed
Problem is, when I try to assign the data, it says I haven't initialized the variable, which is weird, because I did initialize it 3 lines before, var, let and const all throw the same error
Another thing is that outside the if statement, just above it, when console.logging it, it works perfectly, but when console.logging it inside the if statement, it throws that error
I honestly have no idea what's happening here, I can't think of anything that's causing this either, is this a NodeJS bug? I feel like it could be.
const games = JSON.parse(fs.readFileSync("./lib/database/games/chess/chess_games.json"))
console.log(games, 'outside if statement') // Here it outputs just fine
if (games[interaction.guild.id] == undefined) {
console.log(games, 'inside if statement') // Here is where it breaks
games[interaction.guild.id] = {
games: {},
players: {},
amount_of_games: 0
}
fs.writeFileSync("./lib/database/games/chess/chess_games.json", JSON.stringify(games, null, 2));
const games = JSON.parse(fs.readFileSync("./lib/database/games/chess/chess_games.json"))
}
This is the error:
ReferenceError: Cannot access 'games' before initialization
at Object.execute (C:\Users\aschr\Dropbox\Coding\Javascript\entropic_bot\lib\database\bot\commands\chess.js:40:4)
at processTicksAndRejections (node:internal/process/task_queues:96:5)
at async Client.<anonymous> (C:\Users\aschr\Dropbox\Coding\Javascript\entropic_bot\index.js:44:3)

You have two variables with the same name.
Change the name of one of them
The second games is tried to be accessed instead of the first one because of hoisting. That's why you are getting the error

Related

How to use a user's submitted code, and get its errors to have relevant info?

So I'm creating a mod for the singleplayer browser game Cookie Clicker. In my mod I allow the user to insert in their own code to do their own special things to interact with my mod's main function.
However, when the user codes on my custom editor, I want to "test" their code before they save to make sure no errors happen, and if they do, display a error message with what they did and where they did it. Getting the error is easy with a try/catch. But I noticed the error message is:
SynaxError: missing ) after argument list
at new Function (<anonymous>)
at HTMLAnchorElement.save.onclick (chrome-extension://dhdgffkkebhmkfjojejmpbldmpobfkfo/userscript.html?name=Building%2520Sorter.user.js&id=18320655-b018-42e2-8fa5-7fb0cc8d2d70:578:24)
Which isn't helpful for me at all. The most I could salvage from this is the first line. However, that doesn't tell the user at all where the error is located in their code.
the 578:24 that points to the supposed error is:
try{
//code.value is a STRING of the user's code
let func = new Function(code.value);//<-- error points here in my source code.
func.call(null, [[0, 1, 2], Game]);
save.classList.remove('ModBuildingSorter_unsaved');
}
catch(e){
console.dir(e);
}
What I would like to happen is when the user sumbits:
return function(array){
return array.sort(function(building1,building2){
return building1.price - building2.price;
};// missing array.sort closing parenthesis
}
get's ran, I can get a syntax error telling me it's on line 4
Is there a way I can do this? Make the user's code act kinda like it's own file and try running it so I can find out which row & column the error is located?
You could, in theory, run the function from an eval()
i.e.:
try {
let a = "function test(o){console.lo(o)}test('hello');" // Minified function
eval(a)
} catch (e) {
console.log(e)
}
Here is the unminified function for example purposes:
function test(o)
{
console.lo(o) // <-- Error
}
test('hello');
and this returns the error correctly, which is
TypeError: console.lo is not a function
at test (eval at <anonymous> (D:\StackOverflowSandbox\index.js:3:5), <anonymous>:1:26)
Hope I've helped.

Is there a way to override the default JS error messages?

I'm guessing the answer to my question is no, but since I don't know enough about how Error.prototype works I figured it was worth asking: is there any way to change the error messages from the errors in Javascript?
For instance, if I get an error:
TypeError: (intermediate value) is not iterable
is there any way to change things such that I instead get:
TypeError: You expected an array but it wasn't an array dummy!
I thought about using a global error handler and then rethrowing them, but that would only work for uncaught errors. Is there any Error.prototype method I can change (or any other way) to do this?
Not at all important, just curious.
EDIT: Just to clarify two points:
1) I understand how try/catch works, but what I'm asking about is whether there is a way to control the messages generated before the error is thrown/caught (presumably by overwriting a method of Error.prototype).
2) An answer of "no there is no way to do this, all generating of JS error messages is handled internally and the JS code has no way to control it" would be perfectly legitimate (... if that's the case).
You have to override the TypeError class, not one of these methods.
const overridableMessages = [{
search: 'TypeError: (intermediate value) is not iterable',
replace: 'TypeError: You expected an array but it wasn\'t an array dummy!'
}]
class TypeError extends window.TypeError {
constructor (message) {
super(message)
overridableMessages.forEach((overridableMessage) => {
if (this.message === overridableMessage.search) {
this.message = overridableMessage.replace
}
})
}
}
window.TypeError = TypeError
window.onerror = function(msg, url, linenumber) {alert('Error : '+msg+'\nURL: '+url+'\nLine Number: '+linenumber);return true;}
// general error handler
Also:
try {
}
catch(err) {
alert(err); // here put your case with your messages.
}
// routine error handler
HIH,
I hate to answer my own question, but I found this line on the MDN which seems to pretty clearly answer things:
The global Error object contains no methods of its own, however, it does inherit some methods through the prototype chain.
Since the only methods it gets through the prototype chain are toString and toSource (neither of which controls an error's generated message), it appears (unless I'm missing some other mechanism that isn't Error.prototype-related) that there is no way to accomplish what I asked.

Able to Get Value in Console, But Undefined When Called From Function in Angular 2 App

I am running into an issue in my Angular 2 app where I'm getting an undefined error that's not making sense to me. What's more perplexing is that, after getting the undefined error, I can effectively check the exact same value in the console and get it with no issues.
First off, here's a version of the function that DOES work:
public getApplicableResult()
{
if (!this.customer || !this.customer.services || !this.customer.services.getAt(0))
{
console.log('Services not available...');
return;
}
else if (this.customer && this.customer.services && this.customer.services.getAt(0))
{
console.log(this.customer.services.getAt(0));
}
When I run this function I get this in the console for my "console.dir" of my object literal:
CustomerServiceDetails
assignments:(...)
authorizations:(...)
If I then click on "assignments" in the console, I get this expanded result:
assignments:
CustomerAssignmentCollection
count:1
items:Array(1)
So all the data is seemingly there and available.
However, if, in my function, if I were to try and access these nested values more directly - such as the value for "count" above, I get an undefined error. That's what I'm not understanding. Perhaps it's something I misunderstand about how the console works. But if seems to me that if I can access the value for this property in the console, then I should be able to access it directly via my function.
Here's an example of the same function, slightly altered to get the result for "count" within assignments, that returns undefined:
public getApplicableResult()
{
if (!this.customer || !this.customer.services || !this.customer.services.getAt(0).assignments)
{
console.log('Services not available...');
return;
}
else if (this.customer && this.customer.services && this.customer.services.getAt(0).assignments)
{
console.dir(this.customer.services.getAt(0).assignments.count);
}
The specific error I get is:
Cannot read property 'assignments' of undefined;
To add some additional info, assignments is not an array, it's a collection.
Two questions here:
1.) Why isn't my first "if" clause handling the 'undefined' error? How could I adjust it to handle the situation better?
2.) Why can I call the first function, get a result, and then drill down from there in the console to get what I need, but if I try and access a more nested part of the object in the function itself, I get undefined as a result?
One additional detail, I was calling this via Angular's ngAfterViewChecked(). So what that should do, even if it's a timing issue, is return the first "if" else clause result until the value is available, and then it should show the result - i.e., it should execute the "else if" block - because AfterViewChecked() keeps checking. But this isn't happening. I'm just getting the undefined result I mentioned above.

Const behaviour if require fails

Opening the node repl (v6.6.0) and doing:
> const test = require('somethingGuaranteedToFail');
Error: Cannot find module 'somethingGuaranteedToFail'
Now the variable test can neither be redefined, nor has it been properly initialized.
> console.log(typeof test);
ReferenceError: test is not defined
> const test = 1;
TypeError: Identifier 'test' has already been declared
It seems to happen with anything that throws an error during assignment, not just require.
I guess the question is, is this expected behaviour? I would have thought the const variable would at least contain the Error object.
I guess the question is, is this expected behaviour?
Yes. A const cannot be redefined or redeclared. const test declared it, but failed to define it because an error was raised.
I would have thought the const variable would at least contain the Error object.
require does not return an error, it throws one. If you want it, you need to catch it.
Yes, this is expected the behavior. If you throw an exception, the test variable will never initialize. This is also the case for something like
var getTest;
try {
getTest = function(){
return test;
};
throw new Error();
const test = 'a string';
} catch (e){
// ignore the error
}
getTest();
The final call to getTest will attempt to access test, which was never initialized because the exception caused the string value to never be assigned. It will never be assigned the Error object, because the initialization of test is unrelated to the exception.
I don't know if this is a bug, but regardless of whether it's intended or not, this behavior can only occur in a REPL environment.
The reason is that, unlike var, const is block-scoped, but if you try to assign the result of a require statement that throws an exception to it (e.g., when the module resolution fails), an exception will be thrown and execution will leave the scope of the block, so the variable falls out of scope. Since you can't stay in the same scope as the variable is defined after an exception is thrown, you cannot redefine a new const variable in the same scope.
However, in the REPL environment, you don't leave the same scope when an exception fails, therefore you can end up in a situation where a failed const declaration is still in scope, so node refuses to redeclare it.

Uncaught TypeError: Cannot read property 'value' of null, need some direction

I have been trying to figure out this particular problem in my developer tools, but I've had no luck thus far. I have an error on one of my js files that says
Uncaught TypeError: Cannot read property 'value' of null
The following error refers to the 1st variable of dt_version below. The particular thing is if I comment out the first line of code. I get the same error on the following variables of offload1 and offload2. The variable is a number that I am trying to get passed over. I run this function on my body when the page loads...onload=updatetotal();
function updatetotal() {
var dt_version = document.getElementById("dt_version").value-0;
var offload1 = document.getElementById("capacity_offload1").value-0;
var offload2 = document.getElementById("capacity_offload2").value-0;
var offload3 = document.getElementById("capacity_offload3").value-0;
}
If a run an if statement looking for document.getElementByID("dt_version");...it defaults to false..so its not being carried over though on the previous page, I can see its input fine with the value in it. What am I missing here guys?
This error means that the id dt_version does not exist. Check your html to make sure it is there:
var dt = document.getElementById("dt_version");
if (dt){
// do your stuff
}else {
console.log("dt does not exist")
}
Another cause for this error may be- as you are calling the javascript function on page load there is a possible chance that your control is not yet completely rendered to the page. A simple solution is just move that control to the beginning of the page. If it doesn't work then an reliable solution is, call the function inside jquery $(document).ready().

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