Inserting data into an array sequentially

Question

I am currently trying to figure out how to design some sort of loop to insert data into an array sequentially. I'm using Javascript in the Unity3D engine.

Basically, I want to store a bunch of coordinate locations in an array. Whenever the user clicks the screen, my script will grab the coordinate location. The problem is, I'm unsure about how to insert this into an array.

How would I check the array's index to make sure if array[0] is taken, then use array[1]? Maybe some sort of For loop or counter?

Thanks

jfriend00 · Accepted Answer · 2011-06-30 07:00:45Z

3

To just add onto the end of an array, just use .push().

var myArray = [];
var coord1 = [12,59];
var coord2 = [87,23];

myArray.push(coord1);
myArray.push(coord2);

myArray, now contains two items (each which is an array of two coordinates).

Now, you wouldn't do it this way if you were just statically declaring everything as I've done here (you could just statically declare the whole array), but I just whipped up this sample to show you how push works to add an item onto the end of an array.

See https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/push for some reference doc on push.

In case you need to know the array's length when reading the array in the future, you can use the .length attribute.

var lengthOfArray = myArray.length;

edited Jun 30, 2011 at 7:00

answered Jun 30, 2011 at 6:16

jfriend00

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2 Comments

nnnnnn Over a year ago

+1 - even though you edited your post to add the bit about length, thus making my answer (below) redundant (I was typing it up at the same time as you were making your edit).

brymck Over a year ago

It's also worth adding that to remove the last item from an array (return the value and delete it from the array) you can use pop. Their respective functions -- which can be much slower -- for dealing with the beginning of the array are unshift (add to beginning) and shift (return and remove from beginning).

nnnnnn · Accepted Answer · 2011-06-30 07:17:12Z

Using the .push() method as suggested by jfriend00 is my recommendation too, but to answer your question about how to work out what the next index is you can use the array's length property. Because JavaScript arrays are zero-based The length property will return an integer one higher than the current highest index, so length will also be the index value to use if you want to add another item at the end:

anArray[anArray.length] = someValue; // add to end of array

To get the last element in the array you of course say anArray[anArray.length-1].

Note that for most purposes length will give the number of elements in the array, but I said "one higher than the current highest index" above because JavaScript arrays are quite happy for you to skip indexes:

var myArray = [];
myArray[0] = "something";
myArray[1] = "something else";
myArray[50] = "something else again";
alert(myArray.length); // gives '51'
// accessing any unused indexes will return undefined

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