How to add undefined element to array?

Question

It's simple, i want to add an undefined element to an array, lets say i have an array Punkt and i have punkt[0] = x: 15, y:"16s" . As i know for ex. the element will have 4 punkt in total i want to add an undefined element to punkt[3], so that also the others punkt[1] and punkt[2] will become undefined. I need this because somewhere later in my code i do a check for undefined, and throw an error based on this.

Racks is an object that contains an array of objects Punkt

punkt[0] = {
x: 5,
y: "16s" }

What i tried:

racks[trimdevID].punkt[$('#posTable tr:last td:first').text()] = undefined;

Well what happens when you try that? Do you get an error? What's the value of that jQuery `.text()` expression? — Pointy, Dec 03 '13 at 13:30
Why are you prefilling the array? If you try to access `punkt[1]` it will return `undefined`. What benefit is there of putting `undefined` in there? — Matt Ellen, Dec 03 '13 at 13:30
Are you simply trying to empty your array? You shouldn't really ever want to make an array index undefined, you should simply remove that particular index using splice. — Michael Tempest, Dec 03 '13 at 13:31
Nothing happens at the moment :( the .text will return a value that is a number, possibly in a string, i will try casting that — Faarbhurtz, Dec 03 '13 at 13:33
*"i want to add an `undefined` element to `punkt[3]`, so that also the others `punkt[1]` and `punkt[2]` will become `undefined`"* Why? The default value is `undefined`. Adding `punkt[3]` doesn't really do anything for you. It certainly does nothing to change `punkt[1]` and `punkt[2]`. — Blue Skies, Dec 03 '13 at 13:39
You're welcome. FYI, if you want your Array to show a `.length` of `4`, then setting `punkt[3]` would do that, but you can also just do it manually. `punkt.length = 4;` — Blue Skies, Dec 03 '13 at 13:42

Shadow The GPT Wizard · Answer 1 · 2013-12-03T13:49:01.750

2

undefined is built in property of the global object and it's indeed what you need, so such code for example is working:

var arr = [];
arr.push(undefined);
alert(typeof arr[0]);

This means your problem is elsewhere, from quick look it's because you're using non integer index. Try this instead and it should work:

var index = parseInt($('#posTable tr:last td:first').text(), 10);
if (!isNaN(index))
    racks[trimdevID].punkt[index] = undefined;

edited Dec 03 '13 at 13:49

answered Dec 03 '13 at 13:33

Shadow The GPT Wizard

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if(changingPos – Faarbhurtz Dec 03 '13 at 13:40
`undefined` isn't a keyword. – Blue Skies Dec 03 '13 at 13:41
1

@BlueSkies wrong semantics... not a keyword and you can declare local variable with same name but it's still what I meant. Semantics fixed. :) – Shadow The GPT Wizard Dec 03 '13 at 13:49

score 2 · Accepted Answer · edited May 23 '17 at 11:43

You can certainly use the push() routine (see http://www.w3schools.com/jsref/jsref_push.asp). In your example, that would look something like:

// push two undefined elements:
racks[trimdevID].punkt.push(undefined)
racks[trimdevID].punkt.push(undefined)

That assumes that you already have exactly two elements in the array and you want exactly four elements. The more generic version of this is:

var newLength = 4;
for (var idx = racks[trimdevID].punkt.length; idx <= newLength; idx++)
{
   racks[trimdevID].punkt.push(undefined);
}

I believe other similar stack questions also have the same answer. You might look at this question for more examples (How to initialize an array's length in javascript?)

Thanks for the link, initializing array lenght also helps for me — Faarbhurtz, Dec 03 '13 at 13:46

score 1 · Answer 3 · answered Dec 03 '13 at 13:38

1

You can try .push in array

yourArray.push(undefined)
i = 0; //Position Of Undefined
console.log(typeof yourArray[i])

answered Dec 03 '13 at 13:38

Prateek

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How to add undefined element to array?

3 Answers3