Better way to check variable for null or empty string?
// Function for basic field validation (present and neither empty nor only white space
function IsNullOrEmptyString($str){
return ($str === null || trim($str) === '');
}
Is there a standard function to check for null, undefined, or blank variables in JavaScript?
You can just check if the variable has a truthy
value or not. That means
if( value ) {
}
will evaluate to true
if value
is not:
- null
- undefined
- NaN
- empty string ("")
- 0
- false
The above list represents all possible falsy
values in ECMA-/Javascript. Find it in the specification at the ToBoolean
section.
Furthermore, if you do not know whether a variable exists (that means, if it was declared) you should check with the typeof
operator. For instance
if( typeof foo !== 'undefined' ) {
// foo could get resolved and it's defined
}
If you can be sure that a variable is declared at least, you should directly check if it has a truthy
value like shown above.
Best way to check for empty or null value
The expression stringexpression = ''
yields:
TRUE
.. for ''
(or for any string consisting of only spaces with the data type char(n)
)NULL
.. for NULL
FALSE
.. for anything else
So to check for: "stringexpression
is either NULL or empty":
(stringexpression = '') IS NOT FALSE
Or the reverse approach (may be easier to read):
(stringexpression <> '') IS NOT TRUE
Works for any character type including char(n)
. The manual about comparison operators.
Or use your original expression without trim()
, which is costly noise for char(n)
(see below), or incorrect for other character types: strings consisting of only spaces would pass as empty string.
coalesce(stringexpression, '') = ''
But the expressions at the top are faster.
Asserting the opposite is even simpler: "stringexpression
is neither NULL nor empty":
stringexpression <> ''
About char(n)
This is about the data type char(n)
, short for: character(n)
. (char
/ character
are short for char(1)
/ character(1)
.) Its use is discouraged in Postgres:
In most situations
text
orcharacter varying
should be used instead.
Do not confuse char(n)
with other, useful, character types varchar(n)
, varchar
, text
or "char"
(with double-quotes).
In char(n)
an empty string is not different from any other string consisting of only spaces. All of these are folded to n spaces in char(n)
per definition of the type. It follows logically that the above expressions work for char(n)
as well - just as much as these (which wouldn't work for other character types):
coalesce(stringexpression, ' ') = ' '
coalesce(stringexpression, '') = ' '
Demo
Empty string equals any string of spaces when cast to char(n)
:
SELECT ''::char(5) = ''::char(5) AS eq1
, ''::char(5) = ' '::char(5) AS eq2
, ''::char(5) = ' '::char(5) AS eq3;
Result:
eq1 | eq2 | eq3
----+-----+----
t | t | t
Test for "null or empty string" with char(n)
:
SELECT stringexpression
, stringexpression = '' AS base_test
, (stringexpression = '') IS NOT FALSE AS test1
, (stringexpression <> '') IS NOT TRUE AS test2
, coalesce(stringexpression, '') = '' AS coalesce1
, coalesce(stringexpression, ' ') = ' ' AS coalesce2
, coalesce(stringexpression, '') = ' ' AS coalesce3
FROM (
VALUES
('foo'::char(5))
, ('')
, (' ') -- not different from '' in char(n)
, (NULL)
) sub(stringexpression);
Result:
stringexpression | base_test | test1 | test2 | coalesce1 | coalesce2 | coalesce3
------------------+-----------+-------+-------+-----------+-----------+-----------
foo | f | f | f | f | f | f
| t | t | t | t | t | t
| t | t | t | t | t | t
null | null | t | t | t | t | t
Test for "null or empty string" with text
:
SELECT stringexpression
, stringexpression = '' AS base_test
, (stringexpression = '') IS NOT FALSE AS test1
, (stringexpression <> '') IS NOT TRUE AS test2
, coalesce(stringexpression, '') = '' AS coalesce1
, coalesce(stringexpression, ' ') = ' ' AS coalesce2
, coalesce(stringexpression, '') = ' ' AS coalesce3
FROM (
VALUES
('foo'::text)
, ('')
, (' ') -- different from '' in a sane character types
, (NULL)
) sub(stringexpression);
Result:
stringexpression | base_test | test1 | test2 | coalesce1 | coalesce2 | coalesce3
------------------+-----------+-------+-------+-----------+-----------+-----------
foo | f | f | f | f | f | f
| t | t | t | t | f | f
| f | f | f | f | f | f
null | null | t | t | t | t | f
db<>fiddle here
Old sqlfiddle
Related:
- Any downsides of using data type "text" for storing strings?
How do I check for an empty/undefined/null string in JavaScript?
Empty string, undefined, null, ...
To check for a truthy value:
if (strValue) {
// strValue was non-empty string, true, 42, Infinity, [], ...
}
To check for a falsy value:
if (!strValue) {
// strValue was empty string, false, 0, null, undefined, ...
}
Empty string (only!)
To check for exactly an empty string, compare for strict equality against ""
using the ===
operator:
if (strValue === "") {
// strValue was empty string
}
To check for not an empty string strictly, use the !==
operator:
if (strValue !== "") {
// strValue was not an empty string
}
Easiest way to check for null and empty string on a TypeScript number
You can simply use typeof. It will check undefined, null, 0 and "" also.
if(typeof RetailPrice!='undefined' && RetailPrice){
return this.RetailPrice;
}
checking if a string variable has data in it, which one is better !empty() or '!'
empty($var)
vs.!$var
a.k.a.$var == false
The only difference is that empty
does not throw an Undefined variable notice if the variable does not exist, otherwise they're both identical. Now, if you are sure that the variable should exist, use just !
. If the variable may legitimately not exist, use empty
. If you needlessly use empty
, you're just needlessly disabling PHP's error reporting mechanism which may help you catch problems with mistyped variables or logic errors.
Also see The Definitive Guide To PHP's isset And empty.
How to check if a value is not null and not empty string in JS
If you truly want to confirm that a variable is not null and not an empty string specifically, you would write:
if(data !== null && data !== '') {
// do something
}
Notice that I changed your code to check for type equality (!==
|===
).
If, however you just want to make sure, that a code will run only for "reasonable" values, then you can, as others have stated already, write:
if (data) {
// do something
}
Since, in javascript, both null values, and empty strings, equals to false (i.e. null == false
).
The difference between those 2 parts of code is that, for the first one, every value that is not specifically null or an empty string, will enter the if
. But, on the second one, every true-ish value will enter the if
: false
, 0
, null
, undefined
and empty strings, would not.
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