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JavaScript The Solution

Posted by B.B. Groeneveld
B.B. Groeneveld
2,826 Points

When to choose which Logical Operator in this challenge? An AND operator works as well.

Hi everyone,

It seems that my program is running perfectly fine, though I use an AND logical operator in stead of the OR operator, used by Dave in the video. How come it still works? I thought that when using a AND operator, the arguments have to be both isNaN?

Here my written syntax:

// declare program variables
var num1;
var num2;
var message;

// announce the program
alert("Let's do some math!");

// collect numeric input num1
num1 = prompt("Please type a number");
num1 = parseFloat(num1);

//collect numeric input num2
num2 = prompt("Please type another number");
num2 = parseFloat(num2);

//handling error isNaN for input
if ( isNaN( num1 && num2 )) {
  alert("At least one of the values you typed is not a number. The page will reload.");
  window.location.reload();
}

// handling error 0
if ( num2 === 0 ) {
  alert("Division by 0 is not allowed in Math. Please give a correct number.");
  window.location.reload();
}

// build an HTML message
message = "<h1>Math with the numbers " + num1 + " and " + num2 + "</h1>";
message += num1 + " + " + num2 + " = " + (num1 + num2);
message += "<br>";
message += num1 + " * " + num2 + " = " + (num1 * num2);
message += "<br>";
message += num1 + " / " + num2 + " = " + (num1 / num2);
message += "<br>";
message += num1 + " - " + num2 + " = " + (num1 - num2);

// write message to web page
document.write(message);
Antti Lylander
Antti Lylander
9,686 Points
Antti Lylander
Antti Lylander
9,686 Points

Have you tried giving a string (not a number) as an input? Otherwise it does not matter what you put there..

2 Answers

Jacob Mishkin
Jacob Mishkin
23,118 Points

You want both inputs to be a number, and if not throw an error to the user, which you did.

I haven't seen the video, but from the code you are using the OR (||) operator here would not work. The OR operator will check the first expression and if true will execute the code, and will not look at the second expression, unless the first expression is false, then it will look at the second expression.

With the AND (&&) BOTH expressions need to be true in order to execute the code, which you have.

You're good.

Here are some examples using operators: 

using &&

a1 = true  && true       // t && t returns true
a2 = true  && false      // t && f returns false
a3 = false && true       // f && t returns false

using ||

o1 = true  || true       // t || t returns true
o2 = false || true       // f || t returns true
o3 = true  || false      // t || f returns true

operators

Antti Lylander
Antti Lylander
9,686 Points
Antti Lylander
Antti Lylander
9,686 Points 
if ( isNaN( num1 && num2 )) {
  alert("At least one of the values you typed is not a number. The page will reload.");
  window.location.reload();

alert should be shown when either num1 OR num2 is not a number. Now it will be only shown if both are not numbers. Now, if you only give numbers, everything will seem just fine.

Konrad Dziekonski
Konrad Dziekonski
7,798 Points
Konrad Dziekonski
Konrad Dziekonski
7,798 Points

Hey

I get a bit cofused in a video there was that this kind of shortcuts cannot be used and it should be

if (isNaN(num1) || isNaN(num2))

so apart from || and && is this:

'if ( isNaN( num1 && num2 ))' and 'if ( isNaN( num1 || num2 ))'

a valid and working piece of code? does the browser execute it this same way as

if (isNaN(num1) || isNaN(num2)) and if (isNaN(num1) && isNaN(num2))

but its just a bad practice?

thanks