How to right this syntax correctly:
if (tipoTropaPrioritaria[m] || troopsCount[m] || availableTroops[m]) == ("null" || "undefined") {
...
}
(to check if any of the first 3 variables is null or undefined)
views:
388answers:
7
+2
A:
Use:
if (tipoTropaPrioritaria[m] == null || troopsCount[m] == null || availableTroops[m] == null ||
tipoTropaPrioritaria[m] == undefined || troopsCount[m] == undefined || availableTroops[m] == undefined) {
// ...
}
EDIT: It's probably better to use the === (threequals) operator in this case.
if (tipoTropaPrioritaria[m] === null || troopsCount[m] === null || availableTroops[m] === null ||
tipoTropaPrioritaria[m] === undefined || troopsCount[m] === undefined || availableTroops[m] === undefined) {
// ...
}
or:
if (null in {tipoTropaPrioritaria[m]:0, troopsCount[m]:0, availableTroops[m]:0} || undefined in {tipoTropaPrioritaria[m]:0, troopsCount[m]:0, availableTroops[m]:0}) {
Lucas Jones
2010-05-24 21:11:10
You should use `typeof foo == "undefined"` as undefined can be set as a variable with a different value.
Sean Kinsey
2010-05-24 21:18:59
what is typeof foo and why should I use it?
Fernando SBS
2010-05-24 21:36:13
i´m going to use if (null in {tipoTropaPrioritaria[m]:0, troopsCount[m]:0, availableTroops[m]:0} || undefined in {tipoTropaPrioritaria[m]:0, troopsCount[m]:0, availableTroops[m]:0})should I use typeof foo ??
Fernando SBS
2010-05-24 21:41:14
i´m getting error: missing : after property id
Fernando SBS
2010-05-24 21:47:06
Ah. I was worried this trick might not work with the more complicated expressions. Give me a couple of minutes and I'll try to find a work-around.
Lucas Jones
2010-05-24 21:53:45
I don't think there's a simple workaround - I'd use one of the simpler versions either in my answer or another. http://pastebin.com/8Q5NJCjL contains a possible one if you really want to use the second way I demonstrated, but it's more of an academic exercise than something that should actually be used.
Lucas Jones
2010-05-24 21:59:25
Your object property example won’t work: `var x=null; x in {x:0}` yields *false*.
Gumbo
2010-05-24 23:19:21
+1
A:
This is the best way to do what you want
if (!tipoTropaPrioritaria[m] || !troopsCount[m] || !availableTroops[m]) {
...
}
The ! operator coerces the result into a boolean that can be tested for (null and undefined becomes false), and with the ! in front false is negated into true.
The other way to do it is to test each expression against null and undefined.
function isNullOrUndefined(val) {
return (val === null || typeof val == "undefined");
}
if (isNullOrUndefined(a) || isNullOrUndefined(b) ... ) {
And so you know it, the correct way to test for undefined is
if (typeof foo === "undefined") {...
Sean Kinsey
2010-05-24 21:12:14
Be careful with the non-specific test. A non-null boolean value of **false** will be treated the same as **null** unless you test for undefined/null.
John Fisher
2010-05-24 21:14:43
The only problem with this is that `availableTroops[m]` might legitimately be 0, which might need a different behavior than null or undefined.
Gabe
2010-05-24 21:15:23
@Claudio: it is guaranteed that `typeof` returns a string, so `===` is not needed.
Sean Kinsey
2010-05-24 21:16:09
if I use if (!tipoTropaPrioritaria[m] || !troopsCount[m] || !availableTroops[m]) { ...}I believe I can have problems if the value of one of the variables is 0. Am I wrong?
Fernando SBS
2010-05-24 21:42:35
No, you are absolutely right; so in this case you should go for a function like `isSet` or `isNullOrUndefined` mentioned in the answers.But in your case, will `0` be treated different than not being set? Often 0 and not set can be treated as the same.
Sean Kinsey
2010-05-24 21:48:09
A:
if (tipoTropaPrioritaria[m] && troopsCount[m] && availableTroops[m]) { }
else { /* At least ones is undefined/null OR FALSE */ }
if (tipoTropaPrioritaria[m] == null || troopsCount[m] == null || availableTroops[m] == null)
{ /* One is null. */ }
John Fisher
2010-05-24 21:13:23
@Matt That's what the "OR FALSE" comment was meant to address (zero, false, null)
John Fisher
2010-05-24 21:53:32
+1
A:
The way to do is:
if ((tipoTropaPrioritaria[m] == null || tipoTropaPrioritaria[m] == undefined)
|| (troopsCount[m] == null || troopsCount[m] == undefined) ||
(availableTroops[m] == null || availableTroops[m] == undefined)) {
...
}
Web Logic
2010-05-24 21:13:42
+3
A:
You could define a small helper function that does the check and then use it on all the values:
function notset(v) {
return (v === undefined) || (v === null);
}
if (notset(tipoTropaPrioritaria[m]) || notset(troopsCount[m]) ||
notset(availableTroops[m])) {
...
}
sth
2010-05-24 21:15:41
Just out of curiousity, would either of these work? http://pastebin.com/eA3L18qZ
Lucas Jones
2010-05-24 21:52:31
@Lucas: I guess those should work, but probably it would be more readable to use a named function instead of defining it "inline".
sth
2010-05-24 22:16:20
+1
A:
If you do this a lot you can create a helper function
function isNullOrUndef(args) {
for (var i =0; i < arguments.length; i++) {
if (arguments[i] == null || typeof arguments[i] === "undefined") {
return true
}
}
return false
}
if (isNullOrUndef(tipoTropaPrioritaria[m], troopsCount[m], availableTroops[m]))
...
Alex K.
2010-05-24 21:16:42
A:
if you want to check if they are null or undefined you can write
if (!tipoTropaPrioritaria[m] || !troopsCount[m] || !availableTroops[m])
both null and undefined are falsely values. Then this will only be true if none of this are null or undefined.
Please consider that there are other falsely values as well:
- 0
- empty string
- NaN
Dani Cricco
2010-05-24 23:00:40