JavaScript中的多个逻辑运算符

Question

I want to check the following

1: Is xa number
2. If x is less that 5 or greater than 15, sound alert 3. If all is ok, callMe()

var x = 10;
if (isNaN(x) && ((x < 5) || (x > 15))) {
alert('not allowed')
}
else
{
callMe();
}

What am I doing wrong?

Answer 1

var x = 10;
if (isNaN(x) || (x < 5) || (x > 15)) {
    alert('not allowed')
}
else
{
    callMe();
}

This way, if x is not a number you go directly to the alert. If it is a number, you go to the next check (is x < 5), and so on.

Answer 2

All the other answers about the && vs || are correct, I just wanted to add another thing:

The isNaN() function only checks whether the parameter is the constant NaN or not. It doesn't check whether the parameter is actually number or not. So:

isNaN(10) == false
isNaN('stackoverflow') == false
isNaN([1,2,3]) == false
isNaN({ 'prop' : 'value'}) == false
isNaN(NaN) == true

In other words, you cannot use it to check whether a given variable contains a number or not. To do that I'd suggest first running the variable through parseInt() or parseFloat() depending on what values you expect there. After that check for isNaN() , because these functions return only numbers or NaN . Also this will make sure that if you have a numeric string then it is also treated like a number.

Answer 3

var x = 10;
if (isNaN(x) || (x < 5) || (x > 15)) {
    alert('not allowed')
}
else
{
    callMe();
}