I am trying to get a comparison operator to work, without success. The operator compares two arrays to ensure they are identical.
if (($(array_1).not($(array_2)).length === 0 && $(array_2).not($(array_1)).length === 0)) {
alert("all matches dropped");
}
The code works of course with 'true' in place of the comparison.
if (true) {
alert("all matches dropped");
}
The strange part is that the comparison returns 'true' when entered into the console:
console.log($(array_1).not($(array_2)).length === 0 && $(array_2).not($(array_1)).length === 0)
----> true
Any ideas what may be wrong? Thanks.
It should be:
if($(array_1).not(array_2).length === 0 && $(array_2).not(array_1).length === 0)
Instead of:
if (($(array_1).not($(array_2)).length === 0 && $(array_2).not($(array_1)).length === 0))
Here $(array_1).not(array_2).length and ($(array_1).not($(array_2)).length both are not the same thing.
Related
I am validating my time in this way
if (
timeInMins != 0 &&
timeInMins != "0" &&
timeInMins != undefined &&
timeInMins != "undefined" &&
timeInMins != null &&
timeInMins != "" &&
!isNaN(timeInMins)
) {
timeInMinsCumulative += parseFloat(timeInMins);
}
Is there any way to make this ugly if-check to sophisticated code?
There are 6 falsy values in javascript: undefined, null, NaN, 0, "" (empty string), and false of course.
So, you can just write
if (timeInMins && timeInMin !== '0') {
timeInMinsCumulative += parseFloat(timeInMins);
}
This uses the coercion behavior of JavaScript and the logical AND operator to simplify your code. The following is very nearly equivalent to your code, but it will also guard against the arguments false and 0n.
if (timeInMins &&
timeInMins !== '0' &&
timeInMins !== 'undefined') {
// whatever
}
Questions for you: do you really expect to ever get the string 'undefined' passed to you? Why do you want to guard against '0' being sent to parseFloat? Are you sure parseInt is not what you want?
It seems you want to check if timeInMins is precise Number type or not.
function isValidNumber(num) {
return typeof num === "number" && !isNaN(num);
}
console.log(isValidNumber(""));
console.log(isValidNumber(undefined));
console.log(isValidNumber(NaN));
console.log(isValidNumber("undefined"));
console.log(isValidNumber(true));
console.log(isValidNumber(false));
console.log(isValidNumber(0));
console.log(isValidNumber("0"));
console.log(isValidNumber(1.234));
Whats the difference between (a==1 || b==1) and ((a || b)==1)
this code block works right
if(userName==="" || userAge==="" ){
addErrorBool(true);
return;}
but this one not
if((userName || userAge)==="" ){
addErrorBool(true);
return;}
whats does the second one do?
a || b will evaluate to a, if a is truthy, otherwise it'll evaluate to b. So ((a || b)==1) will take whichever value that was and compare it against 1.
For example
(0 || 5) == 1
// equivalent to
(5) == 1
(1 || 2) == 1
// equivalent to
(1) == 1
For what you want, use .some instead, if you want to keep things DRY.
if ([userName, userAge].some(val => val === '')) {
addErrorBool(true);
return;
}
And then you can add as many items to the array .some is called on that you want.
(userName || userAge)==="" means:
(userName || userAge): if userName is truthy, use this value. Otherwise use userAge
==="": compare whichever object was chosen above, and compare that this is a string with no contents.
userName==="" || userAge==="" means:
userName==="": compare userName to see if it is a string with no contents
if it is, the result is true, otherwise:
userAge==="": compare userAge to see if it is a string with no contents
if it is, the result is true, otherwise the result is false
It is slightly hard to explain but I want to do something that looks like this:
if(a === 4 && b === true && c === "words" || "numbersandwords")DoSomething();
but it ends running without it matching the first operators. I want to know how to have the last operator except 2 different inputs while still making sure the other criteria are met before running.
You just need to use parentheses, e.g.:
if(a == 4 && b == true && (c == "words" || c == "numbersandwords")) { DoSomething(); }
Just use a few brackets to separate your or parts and the and parts, and add the c === before the last string. Without that equality part at the end, the 'numbersandwords' string always equates to true.
if(a === 4 && b === true && (c === "words" || c === "numbersandwords")){
DoSomething();
}
In JavaScript, like other languages, every operator (like && and ||) has a precendence that determines the order in which it's evaluated. && has higher precedence than ||, so it's evaluated first. Therefore, every term on the left is anded together. Even if they are all false, however, the overall result is true because it's ored with "numbersandwords", which evaluates to true (as does everything except 0, -0, null, false, NaN, undefined, or the empty string). The first thing you need to do is actually compare something (presumably c) to it. Then you can change the order of evaluation using parentheses, which has higher precedence than anything else:
if(a === 4 && b === true && (c === "words" || c === "numbersandwords")) DoSomething();
Alternatively, you can break the test up into several if statements if you may want to eventually do something slightly different based on the value of c (or it just better expresses your intent):
if(a === 4 && b === true)
{
if(c === "words" || c === "numbersandwords")
{
DoSomething();
}
}
Code:
if (!IDTextField.value && !FirstNameField.value &&
!LastNameField.value && !DateOfBirthField.value!GenderField.value) {
alert('No criteria Added');
return;
}
The alert is not called when all the text fields are blank.
You're missing the && between the last two criteria
It should be:
if (!IDTextField.value && !FirstNameField.value &&
!LastNameField.value && !DateOfBirthField.value && !GenderField.value)
In cases like this, it makes a lot of sense to format your if statement like this:
if ( !IDTextField.value
&& !FirstNameField.value
&& !LastNameField.value
&& !DateOfBirthField.value
&& !GenderField.value)
If you do it this way, you can't make the mistake you just made.
xbonez got it right. You are missing && between last two expression.
For something not so important, I would like to get all expressions evaluated using || and then add negation using !, rather than negating all expression and evaluate them with &&. This can make this expression a little faster, if am not wrong.
if (!(IDTextField.value || FirstNameField.value ||
LastNameField.value || DateOfBirthField.value || GenderField.value)) {
alert('No criteria Added');
return;
}
Tell me what you all think??
What is this little abomination?
... !DateOfBirthField.value!GenderField.value
I think that should be:
... !DateOfBirthField.value && !GenderField.value
You should write your code like this
if (!IDTextField.value && !FirstNameField.value &&
!LastNameField.value && !DateOfBirthField.value && !GenderField.value) {
alert('No criteria Added');
return;
}
You're missing the && between the last two criteria
the && is missed ,add it and try ,should work if no other errors exist
I have absolutely no idea why this is not working. Makes no sense to me.
This returns a "syntax error: parse error":
if ($(this).attr("id") === 'search' || opening = true) return false;
For good measure, I also tried the following, which yielded the same result:
if (1 = 1 && 2 = 2) { return false; }
There are three different operators at play:
=: assignment
==: equality
===: strict equality
= actually modifies a variable, so you shouldn't use it inside if statements. That is, you should use ... || opening == true) instead of ... || opening = true).
In JavaScript = is used to assign values, while == and === are used to compare them.
When you put opening = true in your if statement, you aren't checking if opening is true, you are setting opening to true. Try using == instead.
For example,
var x = 5;
if (x == 10) {
alert("x is 10");
} else {
alert("x isn't 10");
}
will display "x isn't 10", while
var x = 5;
if (x = 10) {
alert("x is 10");
} else {
alert("x isn't 10");
}
will display "x is 10".
the first example should read:
if ($(this).attr("id") === 'search' || opening == true) return false;
and the second:
if (1 == 1 && 2 == 2) { return false; }
Note the double equals (==) sign for logic equals is not the same as the single equals (=) sign, that handles variable assignment.
You have an error in your condition
if ($(this).attr("id") === 'search' || opening = true) return false;
should be
if ($(this).attr("id") === 'search' || opening == true) return false;
the problem is with the equals sign
= is different to ==
the first one is the assignment operator. the second one is for comparison
When you test like this:
opening=true;
What you are really doing is setting opening to the value of true. Use == instead.
Finally, order of operations, even if correct, can get confusing. Put parenthesis around each part of the comparison.
if (($(this).attr("id") === 'search') || (opening == true)) return false;
My guess is that === does not exist.
== is for testing equality
so if ($(this).attr("id") === 'search' || opening == true) return false;
should be if ($(this).attr("id") == 'search' || opening == true) return false;