How can I loop through an array object and check each element to see if one is defined?

Question

I have an array object that looks like this:

var myArr = [undefined, undefined, undefined, undefined, undefined];

How can I loop through the array object and call a function if any one of the elements in the array is defined and not null?

Do you mean "defined" in the sense of the Array member exists, or "defined" in the sense of "exists, and not `undefined`"? You also then say "not null", so are you saying you also want a `null` check? — cookie monster, Mar 22 '14 at 15:07

score 2 · Accepted Answer · answered Mar 22 '14 at 14:55

If you don't care what the valid value is:

var myFunction = function(){console.log("array has valid values");};
var myArr = [undefined, undefined, undefined, undefined, 2];
var hasUndefined = myArr.some(function(item){
    return typeof item !== "undefined";
});
if (hasUndefined){
    myFunction();
}

If you need to find out what the valid items are:

var myFunction = function(validItems){
    console.log("array has valid values, and here they are:",validItems);
};
var myArr = [undefined, undefined, undefined, undefined, 2];
var validItems = myArr.filter(function(item){return typeof item !== "undefined";})
if (validItems.length){
    myFunction(validItems);
}

score 1 · Answer 2 · edited May 23 '17 at 12:11

1

var myArr = [null,undefined,4,5];

for (var i in myArr) {
    if (myArr[i]) {
        //Do something..
        return;
    }
}

I've also seen this which seems a very nice way.

[null,undefined,4,5].every(function(e) {
    if (e) {
        //Do something..
        return false;
    }
    else return true;
});

Is there a standard function to check for null, undefined, or blank variables in JavaScript?

edited May 23 '17 at 12:11

Community

1
1

answered Mar 22 '14 at 14:49

giannis christofakis

7,151
4
48
63

He wants to avoid null as well and `forEach` will make the function to be executed for every valid element. – thefourtheye Mar 22 '14 at 14:53
You are right I think I misinterpret what he want. But I think `!==` avoids null although I must check. – giannis christofakis Mar 22 '14 at 14:55
Even `return` will not help. – thefourtheye Mar 22 '14 at 14:57

score 0 · Answer 3 · answered Mar 22 '14 at 15:01

0

Try this

function isNotUndefined(item) {
    return typeof item != "undefined";
}

if (myArr.some(isNotUndefined)) {
   //do something
}

In this code I use the Array.prototype.some function to check if any element is defined (to do this I use an extra function called isNotUndefined).

answered Mar 22 '14 at 15:01

exacs

29
3

Doesn't work for me, although it seems a very nice way. – giannis christofakis Mar 22 '14 at 15:38

score 0 · Answer 4 · answered Mar 22 '14 at 15:51

Try this.

var myArr = [undefined, null, 123, undefined, null, 456];//for test
myArrFilterd = myArr.filter(function(x){return x!=null?true:false;});
myArrFilterd.forEach(function(x){console.log(x);/*something you want to do for each element*/});

output:

123
456

How can I loop through an array object and check each element to see if one is defined?

4 Answers4