CODEWITHSUNDEEP
javascriptarraysvariables
user3148364
user3148364

Reputation: 35

Create variable from array keys in JavaScript

Is there a way to make a variable using an array value? For ex.

//Define all Notes in Sharps and Flats
var noteSharp = ["A","A#","B","C","C#","D","D#","E","F","F#","G","G#"];
var noteFlat = ["A","Bb","B","C","Db","D","Eb","E","F","Gb","G","Ab"];

//Make all Major Scales
for (var x=0; x<12; x++){
var noteSharp[x] + "Sharp" = noteSharp[x] + noteSharp[x+2] + noteSharp[x+4] + noteSharp[x+5] + noteSharp[x+7] + noteSharp[x+9] + noteSharp[x+11];
var noteFlat[x] + "Flat" = noteFlat[x] + noteFlat[x+2] + noteFlat[x+4] + noteFlat[x+5] + noteFlat[x+7] + noteFlat[x+9] + noteFlat[x+11];
}

If I do a console.log(CSharp) it says that CSharp is not defined.

In this example I am trying to define a total of 24 variables. Some variable name examples im expecting to get are ASharp , A#Sharp , BbFlat , DFlat. The CSharp and CFlat variable should both be "CDEFGAB"

If this is not possible is it because variables have to be defined before the javascript file is read by the browser at run-time for memory leak security.

Upvotes: 0

Views: 108

Answers (5)

RobG
RobG

Reputation: 147363

If this is not possible

It isn't for local variables without the use of eval.

is it because variables have to be defined before the javascript file is read by the browser at run-time for memory leak security.

No. It's not possible because ECMA-262 specifies that the only way to declare a variable is by a variable declaration statement, which is of the form:

var *identifier* [optional initialiser]

where identifier is a valid identifier, which can't be an expression like:

var 'foo' + 'bar';

The rest of the question has been covered in other answers.

Upvotes: 0

Joseph Myers
Joseph Myers

Reputation: 6552

Change the end of your code to look like this:

for (var x=0; x<12; x++){
    self[noteSharp[x] + "Sharp"] = noteSharp[x] + noteSharp[x+2] + noteSharp[x+4] + noteSharp[x+5] + noteSharp[x+7] + noteSharp[x+9] + noteSharp[x+11];
    self[noteFlat[x] + "Flat"] = noteFlat[x] + noteFlat[x+2] + noteFlat[x+4] + noteFlat[x+5] + noteFlat[x+7] + noteFlat[x+9] + noteFlat[x+11];
}

As a result, you will have global variables with variable names like you want, such as CSharp, which would equal "CDEFGAB"--however, complicated variable names like A#Sharp cannot be written outright as variables, but can still be accessed by using subscript notation, like this self["A#Sharp"] (or window["A#Sharp"] in most cases, although it has traditionally been better style to use self rather than window to refer to the most local window object connected with a script instance).

The other answer looks like it has been finished out by the time I finished typing mine, and it looks good, too.

Upvotes: 0

Joseph
Joseph

Reputation: 119837

If you want to make a global variable, attach it to window

window[variableNameHere] = itsValue;

In your case:

window[noteSharp[x] + "Sharp"] = noteSharp[x] + ...

But it's not good to pollute the global namespace. How about putting it in another namespace:

var sharps = {};
var flats = {};
sharps[noteSharp[x] + "Sharp"] = noteSharp[x]...
flats[noteFlat[x] + "Sharp"] = noteFlat[x]...

//access them
sharps.ASharp;

I quite can't figure out what your code does, but this solution should point you to the right direction.

Upvotes: 4

Dhanu Gurung
Dhanu Gurung

Reputation: 8840

As per my knowledge, in JavaScript there are 2 ways by which you can create dynamic variables:

  • eval Function
  • window object

eval:

var times = 1;
eval("var sum" + times + "=10;");
alert(sum1);

window object:

var times = 1;
window["sum" + times] = 10;
alert(window["sum1"]);

Upvotes: 0

Manish Jangir
Manish Jangir

Reputation: 5437

try the following code

var noteSharp = ["A","B","C"];
for(i in noteSharp) {
 window[noteSharp[i]] = 'value of '+noteSharp[i];
}


alert(A)
alert(B)
alert(C)

This is exactly what you want.

and rewriting it for your code

//Define all Notes in Sharps and Flats
var noteSharp = ["A","A#","B","C","C#","D","D#","E","F","F#","G","G#"];
var noteFlat = ["A","Bb","B","C","Db","D","Eb","E","F","Gb","G","Ab"];

//Make all Major Scales
for (var x=0; x<12; x++){
window[noteSharp[x] + "Sharp"] = noteSharp[x] + noteSharp[x+2] + noteSharp[x+4] + noteSharp[x+5] + noteSharp[x+7] + noteSharp[x+9] + noteSharp[x+11];
window[noteFlat[x] + "Flat"] = noteFlat[x] + noteFlat[x+2] + noteFlat[x+4] + noteFlat[x+5] + noteFlat[x+7] + noteFlat[x+9] + noteFlat[x+11];
}

alert(ASharp);
alert(AFlat);

Upvotes: 0

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