Develop Reference

useEffect does not go to if statements

Do not actually understand why this code part not working as it should.
This useEffect block re-renders on every scrollY position. Also, I see that this code part: console.log(wrapperRef.current.style.opacity); should call if and else if statements, but it does not.
Here is the code:
useEffect(() => {
console.log(wrapperRef.current.style.opacity);
if (wrapperRef.current.style.opacity === 0) {
setIsHidden(true);
console.log("true");
} else if (wrapperRef.current.style.opacity === 1) {
setIsHidden(false);
console.log("false");
}
}, [position]);

As you can see here, style values are strings, but with the === operator you also check for type equality.
This means you check that '0' === 0 which are not the same types and also why your check never enters the if body.
Either check for '0' or use the == operator which does ignore types.

issues with localStorage and saving values

I have a program where I have these strings being added to an array. However, there are many strings that are triggered by a certain condition, which can be met multiple times, however I only want it to be added on the first occurrence. So I have implemented a system where the event of adding the string to the array is triggered by the original condition, and a boolean expression. Here is an example of one of those conditions:
if (count >= 10 && displayMulti == true) {
consoleData.shift()
consoleData.push("Multi available")
displayMulti = false
window.localStorage.setItem("display_multi", String(displayMulti))
updateConsole()
}
When the string is added to the array, the boolean, displayMulti, is set to false so that it will not trigger again. However, upon refreshing the page, it will still trigger. I'm not sure why because I feel like I have saving the values to localstorage correctly. Code is below:
if (window.localStorage.getItem("display_multi") != null ) {
displayMulti = Boolean(window.localStorage.getItem("display_multi"))
} else {
console.log("here")
var displayMulti = true
}
There "here" console log statement is not triggered. So I have no idea why this would keep triggering because I don't see how the boolean is true. I've tested at like so many different points I genuinely have no idea what's wrong. I also don't think those values are affected anywhere else in my code. Any help is appreciated.

Here is a solution that properly parses your string as a boolean. Instead of Boolean(), a conditional (window.localStorage.getItem("display_multi") === 'true')(window.localStorage.getItem("display_multi") === 'true') is used.
if (window.localStorage.getItem("display_multi") != null ) {
displayMulti = (window.localStorage.getItem("display_multi") === 'true')
} else {
console.log("here")
var displayMulti = true
}
if (count >= 10 && displayMulti == true) {
consoleData.shift()
consoleData.push("Multi available")
displayMulti = false
window.localStorage.setItem("display_multi", String(displayMulti))
updateConsole()
}

if statement with more than one condition

I need to check three conditions,
sheet_exists = 1
recalc = 1
qty_total and new_qty_total are not equal
The if statement works well if only the first 2 arguments are used:
if(sheet_exists === 1 && recalc === 'yes'){
//do something
}
But when I try to add he 3rd argument it fails, the actions in the if statement are ignored. I've tried:
if((sheet_exists === 1) && (recalc === 'yes') && (qty_total !== new_qty_total)){
//do something
}
And:
if(sheet_exists === 1 && recalc === 'yes' && (qty_total !== new_qty_total)){
//do something
}
And:
if(sheet_exists === 1 && recalc === 'yes' && qty_total !== new_qty_total){
//do something
}
Where am I going wrong?

Considering you are happy with the behavior of the first two conditions, and not with the last one, the problem must be in the last one.
Pay attention, qty_total !== new_qty_total will return TRUE only when the value or type of qty_total and new_qty_total are different.
If one is an integer 100 and the other is a string '100' then the condition evaluates as TRUE because they differ on the data type. But if they are both integers it will return FALSE, because neither the value nor the type are different.
To make sure the comparison works ok, make sure both variables are the same data type.

Multiple bool var check inside condition

Is this ok way to check if all 4 variables have same value instead of checking each individually?
if (bodovi >= min_bodovi && (Q15,Q16,Q17,Q18) == true)

You can simplify that to:
if (bodovi >= min_bodovi && Q15 && Q16 && Q17 && Q18)
Given that these are boolean variables, their value being TRUE is sufficient for javascript to evaluate each as TRUE. If one of them id false, e.g. Q15 = false, then it will fail

Will validate only the last variable, here if Q18 is true then the condition will just pass even if Q15,Q16,Q17 are false or any one of them false.
(Q15,Q16,Q17,Q18) == true
You can use (Q15 && Q16 && Q17 && Q18)

Javascript variable is null but goes in if-statement

I have a bit of a weird problem. I TRIED to create a jsfiddle but I don't get the same result so I'm sorry I can't share more of what I have.
var parent = id && Number(oldParent) !== 1 ? $('#main_container #item_' + itemId).parent().parent().prev() : null;
This is how I get the parent. It should be null when it isn't needed.
Later, I get this check in the same function:
if (parent && parent != null && !parent.hasClass('.main-group'));
{
console.log(parent == null);
var siblingCount = parent.next().children().length;
if (siblingCount === 0)
{
parent.removeClass('group');
parent.addClass('normal-item');
}
}
So, I check if parent is set (just in case), parent is not null and parent doesn't have the class main-group. This should work, at least I thought, but I get the error:
TypeError: parent is null
On this row:
var siblingCount = parent.next().children().length;
So, that's why I added the console log to see if parent is null. Guess what? The console.log says true. This means parent is equal to null, but it still goes IN the if-statement. I use && so it shouldn't go in the if statement because already one operation is false.
I had others look at it and they couldn't figure it out either.

There is a semicolan at the end which is making it to execute as the statement is terminated and next statement executes.
var parent = null;
if (parent && parent != null && !parent.hasClass('.main-group'));{
alert("Hello");
}
For Debin comment:
var parent = null;
if (parent != null); { alert("Vinoth") }
// The above one is equivalent:
if (parent != null) do nothing ;
alert ("hi");
JavaScript thinks that you have an empty statement and everything to right of it is treated as no longer belonging to the if condition and thus an independent one making it to execute.

You have a ";" at the end of this line
if (parent && parent != null && !parent.hasClass('.main-group'));
This is what is causing the problem.