Develop Reference

Why is my script saying '(' === ')' is true?

I was doing this kata on codewars. The question wants the function to return true if the first argument (string) passed in ends with the 2nd argument (also a string). So I wrote my function and everything worked just fine until it compares ':-)' with ':-(' and returns true.
What is wrong? I'm so confident that my code should work that I don't even know what to search for.
function solution(str, ending){
if (!ending) return true; // if ending is a empty string return true (the question wants that)
let ok;
const strArr = str.split(''), endingArr = ending.split('');
for (let i = 0; i < endingArr.length; i++) strArr.reverse()[i] === endingArr.reverse()[i] ? ok = true : ok = false;
return ok;
}
console.log(solution(":-)",":-("));

Your problem is a misunderstanding of what reverse() does. It does not return a reversed copy of the old array, it reverses the existing array and returns that same array. As a result, you keep reversing the arrays back and forth every iteration of the loop, causing some elements to be skipped and some to be checked twice.
Array.prototype.reverse() on MDN
Edit:
As pointed out by others in the comments, both to the question and this answer, there are in fact multiple problems.
reverse() aside, the loop always sets ok to the result of the last comparison, making the function ignore all previous results.
The easier way to implement this is to remove ok altogether. Instead, return false as soon as a mismatch is detected. If the function runs long enough to exit the loop, it means no mismatch was detected and true can be returned.
Edit 2:
Just as a friendly suggestion:
While both reverse() and ok are real issues with the code, I only noticed the first one the first time around due to the formatting of the code. The ok problem was off-screen due to the line being too long. As such, once I spotted the reverse() issue, I assumed that was it and didn't bother scrolling sideways to see the rest of the code.
I am not going to demand that you write your own code in a certain way, but if you format it properly, it allows others to read it more easily. In essence, you help us to more easily help you.
For instance, this line:
for (let i = 0; i < endingArr.length; i++) strArr.reverse()[i] === endingArr.reverse()[i] ? ok = true : ok = false;
...would have been significantly easier to read as...
for (let i = 0; i < endingArr.length; i++) {
if(strArr.reverse()[i] === endingArr.reverse()[i])
ok = true;
else
ok = false;
}
...or some variation thereof. Here, the problem is significantly more visible and obvious.

The other answer explains many of the mistakes you've made. I wanted to point out just how much you've over-thought your solution.
function solution(str, ending){
if (ending === "") return true; // if ending is a empty string return true (the question wants that)
return str.endsWith(ending);
}
console.log(solution(":-)",":-("));
console.log(solution("foo",""));
console.log(solution("foo","bar"));
console.log(solution("foobar","bar"));
Even my solution above is overengineered, str.endsWith("") always returns true. So this can be simplified further.
function solution(str, ending){
return str.endsWith(ending);
}
console.log(solution(":-)",":-("));
console.log(solution("foo",""));
console.log(solution("foo","bar"));
console.log(solution("foobar","bar"));

How to Check the variable value is [""] in JavaScript

Example:
When I check a variable containing this value [""] it returns false.
var th=[]
th.push("");
if($("#multiselect").val()==th)
It returns always false.
Thank you.
Edit 1:
changed Var to var. It was a typo.
Edit 2:
Actually, the problem I faced was I was trying to get the value from a multi-select input. The multi-select input sometimes returns values as [""] even I haven't selected any values basically it's a plugin. So I was confused and I thought [""] is a fixed primitive value like 1, 10, "bla blah",.. So I tried to compare it with the same array as the right-hand side of the '=' operator.
It was stupid. Now I posted the solution to my problem and I explained my stupidity.

there are two things:
Change Var to var
You can use includes method of Array as:
var th = [] <==== chnage Var to var
th.push("");
if(th.includes($("#multiselect").val())) { <=== you can use includes method of array
// DO whatever you want
}

Make sure var is lowercased.
You are accessing th as an array, so you’ll need to specify the index of the value you are checking: th[0]
Use triple equals, too: .val()===th[0]
Double check the jquery docs if you’re still running into trouble.
Happy coding!

A couple of things to consider:
You have a typo in the code above; var is valid; Var is invalid.
Browser will aptly complain to solve this typo.
You are comparing an array to DOM value; this will always be false.
DOM is a costly process. Unless the value associated is dynamic, its better to read once, store value into a variable and continue processing instead of reading from DOM always.
You could choose to try something on these lines:
let arr = [1,2,3,4];
let domValue = $("#multiselect").val();
arr.push(5);
arr.map((el, ix) => {
if el === domValue return true; //or choose to do something else here.
});

var th=[]; //It is var not Var
th.push("");
if($("#multiselect").val()==th[0]) // change th to th[0]

I am unable to comment so having to use an answer for now. Are you trying to check if an array has any values? If so you can use
if(th.length){
// do something
}
If you want to check a normal variable for empty string you can simply use
if(th == “”){
//do something
}

I found the solution after a couple of days when I posted this question. Now I can feel how stupid this question was.
Anyway, I'm answering this question so it might help others.
Answer to my question:
When two non-primitive datatype objects(which is the Array here) are compared using an assignment operator, it compares its reference of the object. So the object creation of both arrays would be different. If I want to check the array has [""] value, I should do something like the below.
function isArrValEmptyCheck(value) {
return !value || !(value instanceof Array) || value.length == 0 || value.length == 1 && value[0] == '';
}
console.log(isArrValEmptyCheck([""]));//returns true
console.log(isArrValEmptyCheck(["value1"]));//returns false
Sorry for the late response. Thanks to everyone who tried to help me.

object with array type string causing a typeError

The best way to explain this is just to show you.
var condition = 70;
var formnames = new Array("wheelcheckbox1", "wheelcheckbox2","spokecheckbox","spokecheckbox2","tirecheckbox","tirecheckbox2","tirecheckbox3");
formnames.forEach(function(entry) {
console.log(obj.entry);
if(obj.entry == "") {
condition = condition - 10;
}
});
as you can see I used the console log to show how it needs to work
as that works perfect, however, using the array causes an error as
they're strings and not what the obj wants, it wants text without it being a string.
Any ideas?

for..in should not be used to iterate over an array. Consider using forEach instead.

If statement throwing error for nonexistent object

The answer to this question seems like it would be obvious, but I'm always looking to improve my semantics, so bear with me.
I have an array structure with individual items containing X,Y coordinates
var example = new Array();
example.push({x:0,y:0});
In my code I have a set interval that updates my canvas and checks for certain conditions. Including one similar to this
if(example[0].x == other.x && example[0].y == other.y)
{
//do something
}
The issue is that the array is very dynamic, and when the code is first executed the example array is empty. Hence, Chrome throws errors along the lines of "Cannot get property x". To shut up the console, I added a dummy item to the array {x:"~", y:"~"} but it seems really unintuitive. Have I implemented an undesirable data structure? What's a simple way to handle if statements for objects that... don't exist?

Why don't you just check whether the array has elements?
if (example.length && ...)
Or whether the first element is true:
if (example[0] && ...)

if (0 in example
&& example[0].x == other.x && example[0].y == other.y) {
// do something
}
(This works for arbitrary index, not just 0; if you just want to check if the array is non-empty, example.length as shown by melpomene is good.)

You should be able to check on the first-level element (i.e. 'example') - JavaScript usually throws errors like this when you try to access a property of an element that is null or undefined. Like some others have already shown:
if(example[0] && example[0].x === other.x)
The point is though that JavaScript will let you have example[0] and return as you like, but once you try to access that property, you're out of luck:
var example = [];
//undefined
example
//[]
example[0]
//undefined <--- this is a falsy value, will evaluate false in a check
example[0].x
//TypeError: Cannot read property 'x' of undefined

How to distinguish strings from ints in firebug console

I need to distinguish "0" from 0 in Firebug console.log output.
If you type console.log("0") into Firebug console, you'll get 0, same as if you'd typed console.log(0), but I need it to be "0".
In other words, expected output:
console.log("0")
> "0"
console.log(0)
> 0
Actual:
console.log("0")
> 0
console.log(0)
> 0
What is the best solution to this problem?
I've found some workarounds like console.log("%o", "0") or console.log(["0"]), but they are too clumsy and obtrusive to use them everywhere.
I've also tried debug and info without success.
By the way, Chrome console gets it right, but I'm not ready to move to Chrome yet.
I'm thinking about writing some wrapper around console object. I'm not sure how to do it right but I'll try it if there is no other solution.
So, the only solution seems to be that you need make some wrapper that looks like this (based on #wsanville's answer):
var log_orig = console.log;
// No need to check for type, just use %o for everything
// Also, it gets messier for multiple arguments
console.log = function(s) { log_orig('%o', s); }
But then you get the problem with line numbers, as described in How to access line numbers when wrapping Firebug (or similar) Console api
I guess I should file a firebug bug or something, because this can be really critical in some situations.

You could try using console.log(new String('0')) to distinguish from the two cases.
You could also just clobber console.log and encapsulate whichever solution you like best, like this:
var log_orig = console.log;
console.log = function(s)
{
if (s === '0')
log_orig('%o', s);
else
log_orig(s);
}
console.log('0'); //results in "0"

You could use:
console.log("Variable x type is " + typeof(x))
The typeof unary operator determines the type of the variable.
The return values are boolean, number, object, string, or undefined.

console.log(0) will show 0 but in darkblue color
console.log('0') will show 0 in black color
Also you could redefine console.log function:
var _log = console.log;
console.log = function(x) {
if ( Object.prototype.toString.call(x).indexOf('String') != -1 ) {
return _log("'"+x+"'");
} else {
return _log(x);
}
}