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.

Javascript - getElementByID - Error

I am getting this error message in my Javascript.
Unable to get property 'style' of undefined or null reference
document.getElementById('BS2').style.display='block';
What is going on it that sometimes the Element ID is not showing. Is there a way to check if the element is there then do this else, go to the next line of code?
function showb() {
if(document.getElementById('BS1').style.display=='none') {
document.getElementById('BS1').style.display='block';
document.getElementById('BS2').style.display='block';
document.getElementById('BS3').style.display='block';
document.getElementById('BS4').style.display='block';
}
return false;
}
Sometimes the BS1 is showing, BS3 is Showing and BS4... etc.

document.getElementById() returns an object just like anything else. You can assign it to a variable and check the null-ness of the variable:
var bs1 = document.getElementById('BS1');
if (bs1) {
.. do stuff if bs1 is present
} else {
.. do stuff if bs1 is not there
}

AS pointy said in his comment, you should chekc whether there is an element with the desired ID before trying to read its properties. You could use a piece of code like this:
var element = document.getElementById('BS2'); // or any other ID
if (element) { // if no element is found, this evaluates as a logical false.
element.style.display='block';
}
Getting the element in a variable also has the advantage that your code becomes more readable. And since you use this multiple times, you could create a function to encapsulate that logic. Good luck!

Well if the property style hasn't been modified it means that it is just ("")
function showb() {
if(document.getElementById('BS1').style.display) {
document.getElementById('BS1').style.display='block';
document.getElementById('BS2').style.display='block';
document.getElementById('BS3').style.display='block';
document.getElementById('BS4').style.display='block';
}
return false;
}
it is going to be solved just like that because ("") is a falsy value

Javascript return position index of "matched" array within array

Is there an alternative, faster method of returning the position/index of part of an array within another array (where multiple values match)? It's called a lot within my pathfinding algorithm so could do with being as fast as possible.
My current function is:
// Haystack can be e.g. [[0,1,278.9],[4,4,22.1212]]
function coordinate_location_in_array(needle,haystack){
for(n in haystack){
if(haystack[n][0]==needle[0] && haystack[n][1]==needle[1]) return n;
}
return false;
}
// Needle of [0,1]: returns 0
// Needle of [4,4]: returns 1
// Needle of [6,7]: returns false
Edit:
I've been messing around a bit and come up with a (rather ghastly) string manipulation-based method (thereby avoiding the costly for loop). I think it's still slightly slower. Could anybody benchmark these methods?
function coordinate_location_in_array(needle,haystack) {
var str1 = ':' + haystack.join(':');
var str2 = str1.replace(':'+needle[0]+','+needle[1],'*').split('*')[0];
if(str2.length == str1.length) return false;
var preceedingElements = str2.match(/:/g);
return preceedingElements!=null?preceedingElements.length:0;
}
Perhaps with some improvements this second method might provide some performance gain?
Edit 2:
Bench marked all 3 described methods using jsperf.com (initial method is fastest):
http://jsperf.com/finding-matched-array-within-array/3
Edit 3:
Just replaced the for(..in..) loop with a for(..;..;..) loop (since I know that the haystack array will never have "gaps") and performance seems to have significantly improved:
function coordinate_location_in_array(needle,haystack){
for(var n=0;n<haystack.length;n++){
if(haystack[n][0]==needle[0] && haystack[n][1]==needle[1]) return n;
}
return false;
}
I've updated the jsperf page to include this latest method.

If the "haystack" isn't sorted then there isn't a way to make it faster. Not knowing how the elements in a collection are ordered makes finding something out of it linear by nature, because you just have to check each thing.
If you are using this function over the same "haystack" over and over, you could sort the collection, and use the sorting to make it quicker to find the "needle" (look up different sorting and search algorithms to find one that fits your need best, such as using binary search to find the "needle" after haystack is sorted.)

i don't know if its faster, but you can do something like:
[1,2,3,4].slice(0,2).toString() == [1,2].toString()
in your case it would be:
function coordinate_location_in_array(needle,haystack){
for(n in haystack){
if(haystack[n].slice(0,2).toString() == needle.toString()) return n
}
return false;
}
Also found this post, which covers comparison of JS arrays: compare-two-arrays-javascript-associative
Cheers
Laidback

Using a for(..;..;..) loop rather than a for(..in..) loop made the biggest difference.
(See Edit 3 at the end of the question)

Seems to me this is just a substring search but with numbers instead of characters being the components of the string. As such, Boyer-Moore could be applicable, especially if your needles and haystacks get big.

Trying to get some jQuery functions to run in order. Is callback the issue?

I'm trying to do some things in order, and I'm having some trouble.
When the button with the id #sub_button is clicked,
Make sure each element with class ".verify" has it's own object value (see code)...
... if not, blur that element (will run some other code and create an object for it).
AFTER the above IF check is COMPLETE (now all elements should have an object), THEN run function "isitgood". (The "isitgood" function is running before all elements get their object values, which is done on blur)
$("#sub_button").click(function() {
$(".verify").each(function(){
objtitle = $(this).attr('id');
if (!myObj[objtitle]) {
$("#"+objtitle).blur(); // Define anything undefined
}
}); // end each
isitgood();
}); // end click function
function isitgood(){
if (myObj.login_id == "ok" && myObj.email == "ok") {
// submit the form
} else {
// shows error
}
}
Also, once I get this executing in the right order, it would be nice to do some sort of .each loop to check if all the object values == "ok" instead of specifying all of them in the function. All of the names of the objects (ie. login_id, email) are the ID attr of any element with class name .verify.

Well, you could do a quick index check in the click callback:
var sub_buttons = $("#sub_button");
sub_buttons.click(function() {
$(".verify").each(function(index){
objtitle = $(this).attr('id');
if (!myObj[objtitle]) {
$("#"+objtitle).blur(); // Define anything undefined
}
if (index == sub_buttons.length - 1)
isitgood();
}
}); // end each
}); // end click function
This will check if you're on the last element in the jQuery object, and if so, will run the isitgood() function. This way, you make sure that you're finished with the $.each method before executing isitgood()

Javascript is asynchronous. Your isitgood() will always fire while .each is still doing it's thing.
That said from your code it's not clear what you're trying to accomplish. The way you're using .each seems to indicate that you have multiple of the same ID attributes on your tags. That won't work, IDs have to be unique. Also you seem to be mixing jQuery and regular Javascript. Use one or the other. Actually just use jQuery, you'll save yourself time and effort!
If you do have unique ids then you shouldn't need the .each at all. Just check the appropriate ids with your if statement.
Please provide more of your code and i can update this with a better answer. For instance what does your myObj look like? How do elements of it get the value of ok? It doesn't seem to get set within your call to .each().