Renaming Array with Variable

Question

One of the problems with teaching yourself how to code is that you miss some things that might be fairly simple:

I have written a function which takes text files (e.g. "someData1.txt", "someData2.txt" etc.) turns their contents into an array ("myArray"), and extracts their title as a variable ("fileName").

I am at the stage where I have parsed the filenames and the arrays, but I would like to rename each array with the variable, so that the first array becomes "someData1", and so on. I already have a bunch of code which will do various things with each different array, so it would useful if I could name them the way I wish.

I thought I could use valueOf to do it, as in

fileName.valueOf() = myArray;

but that does not work. So how do I do this?

Thanks!

• epascarello: huh? I have no clue what the final outcome is supposed to be... And that is not how you use valueOf

Answer 1

Probably the easiest way would be to use an object and then use array notation to assign keys to it. Let me show you:

var myObj = {};
myObj.someProperty = 1;

is the same as

myObj['someProperty'] = 1; // note the quotes

So, that makes possible to use variable names as keys. In your example:

var fileName = 'someData1';
var myObj = {};
myObj[fileName] = myArray; // myArray being file contents from your example

and now when you want to access the contents, you can simply do:

myObj.someData1

or:

myObj['someData1']

Just make sure you have no duplicate file names and you're good to go.

Answer 2

What you want to do is defining a variable name dynamically.

It is not possible in Javascript though, but you can be tricky. You have then two options :

1. Use the global scope object to store your variables (not a good practice) :

global[variableName] = array;

And then you will be able to access it in the scope :

global['toto'] = 42;
console.log(toto);
=> 42

This is NOT a good practice but is the only way to define a variable in the scope dynamically.

2. Use an object to store it :

var myArrays = [];
myArrays[variableName] = array;

In each case you define in fact a property of an object.

You have to keep in mind that :

myArrays['toto'] = 42;

is the same that :

myArrays.toto = 42;

So to access your array, just do :

myArrays.toto

• Jason Sperske: I am unfamiliar of any global object called global (source). If you assign a value to a variable that does not have a functionally scoped var then it will be hoisted to the global scope.
• kube: Yes I know it is not a good practice at all to use the global object, but it is the only solution to have a variable literally defined in scope, not as a property of an object.
• Tyler330: Thanks! This did occur to me, but I thought there might be some more direct way of doing it. The list of files is not too long, so this will work.
• pawel: @JasonSperske global refers to the global scope in Node.js, very much like window in web browsers. PS. If I need to set global vars I wrap my code in (function(global){ ... }(this)) so I don't have to care how to reference the global scope in given environment.
• kube: Thanks pawel for the precision.