Javascript Arrays

by HSG on Nov 04, 2012 in JavaScript Tutorial

Every programming language has a mechanism to allow the programmer to create variables which hold custom data entered in by either the coder themselves or by the user of the application.

Regardless of whether you’re new to programming or not, you will have used variables and you should understand that in javascript they can hold any value such as a number or a string of text.

There is also another type of variable called an Array. Now, depending on who you talk to, some will say an array is actually an object, while others say it is a variable. Neither one is wrong but for the sake of simplicity we’ll refer to it as a variable.

Now, arrays are special because they can hold multiple values as opposed to standard variables which can only hold a single value at one time. If you can, try and imagine that your computer’s memory is made up of thousands of little boxes, and each of those boxes has an address which javascript will use to retrieve the array values when needed.

Take a look at the following code:

          var myArray = new Array();

          myArray[0] = “hi”;

          myArray[1] = “there”;

          myArray[2] = “Number”;

          myArray[3] = “1”;

    

Let’s analyse the code above: On line one we use the var keyword to create our array. You will also notice on the same line we use the keyword new which tells javascript we’re creating a new object also.

The remaining lines pass the values ‘hi’,’there’,’number’,’1’, to each element in the array. One thing to keep in mind is that an array can have as many elements as needed, and although we are creating ours manually there are ways to pass values to an array more automatically by using looping structures but that is beyond the scope of this tutorial and will be saved for another day.

If you look a little closer at the code you will notice that the first element of our array starts with zero instead of one. In all programming languages array elements always start at zero and move upwards.

If you wanted to create an array with say three elements then you would count from 0 to 2, and likewise if you wanted to create an array with ten elements then you would count from 0 to 9. It is important to keep this in mind when you’re working with arrays that way you do not get errors when you try to iterate over them using loops or other methods to access each element.

Now if you want to access the values of each array element you would do something like the following:

     document.write(myArray[0] + "
");

Obviously you would need to replace the number in the square brackets to access the value at that element. So for example if you had a three element array you could write the following:

 document.write(mycars[0] + "
");

document.write(mycars[1] + "
");

document.write(mycars[2] + "
");

Arrays do take a little getting used to, but once you start using them you will wonder how you ever managed to get by without them.

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