I want to run a code only if the argument[0].recordCount
is greater than zero or is NOT undefined. However, the code is ran when the argument[0].recordCound
alert shows undefined.
if(arguments[0].recordCount > 0 &&
arguments[0].recordCount !== 'undefined')
{ //if more than 0 records show in bar
document.getElementById('totalRecords').innerHTML =
arguments[0].recordCount + " Records";
}
How can I test for undefined here?
I want to run a code only if the argument[0].recordCount
is greater than zero or is NOT undefined. However, the code is ran when the argument[0].recordCound
alert shows undefined.
if(arguments[0].recordCount > 0 &&
arguments[0].recordCount !== 'undefined')
{ //if more than 0 records show in bar
document.getElementById('totalRecords').innerHTML =
arguments[0].recordCount + " Records";
}
How can I test for undefined here?
Share Improve this question edited Jul 25, 2020 at 8:28 Brian Tompsett - 汤莱恩 5,89372 gold badges61 silver badges133 bronze badges asked Jul 22, 2010 at 18:11 Asim ZaidiAsim Zaidi 28.4k49 gold badges138 silver badges224 bronze badges3 Answers
Reset to default 7When using undefined
as a string you need to do so with the typeof
operator.
Also, you should be checking if it's defined before any other checks on the property.
if ( 'undefined' != typeof arguments[0].recordCount && arguments[0].recordCount > 0 )
undefined
is a keyword a global variable with constant value, use it without quotes:
if(arguments[0].recordCount > 0 && arguments[0].recordCount !== undefined)
But actually it would be sufficient to test only the first condition:
if(arguments[0].recordCount > 0)
because if recordCount
is larger than zero, it is defined anyway.
More mon is to switch the conditions and test first whether it is defined, to avoid possible errors in the following tests (not sure if this is necessary here):
if(arguments[0].recordCount !== undefined && arguments[0].recordCount > 0)
To check for a variable to be not null and not undefined,
if(thatVariable)
is enough though implicit conversion can cause problem for some cases where thatVariable is empty string, or a boolean, or number 0. If implicit conversion is not the case for our variable, the following would do,
if(arguments[0].recordCount && arguments[0].recordCount > 0)
But the following would be problematic,
if(arguments[0].recordCount !== undefined && arguments[0].recordCount > 0)
Consider,
var undefined = 'surprise' //possible since undefined is not a keyword
if(arguments[0].recordCount !== undefined && arguments[0].recordCount > 0)
Now this 'if' will break even though recordCount is undefined.
One more thing: if(a != null)
will also check undefined due to implicit conversion. Hence if(a != null && a != undefined)
is redundant