javascript: trouble calling function argument

Question

I am having trouble calling an arguement in the functin below.

function makeScales(size,note1,note2,note3,note4,note5,note6,note7,note8){
    for(var z=0; z<size; z++){
        if(semis=="Sharps"){
            notes = notes + " - " + noteSharp["note" + z];
        } else {
            notes = notes + " - " + noteFlat["note" + z];
        }
    }
}

I went through many debugging procedures and found that my error en-lies with noteSharp["note" + z] more specifically "note" + z . For example if i do console.log(noteSharp[note1]) i get the desired result and i set z to 7 so i can see that its populating appropriately but I get undefined for my results. Any help would be greatly appreciated.

Answer 1

"note" + z will give you a string like "note1" not an identifier.

If you want to access a piece of data by an index, then put it in an array, not in a variable with a number in its name.

For example:

function makeScales(size, notes) {
    //...
    notes = notes + " = " + noteSharp[ notes[z] ];
    //...
}

makeScales( "some size", [ "foo", "bar", "baz" ] );

Alternatively (and I wouldn't recommend this approach as it mixes different kinds of data in a single data structure), you can use the arguments object.

notes = notes + " - " + arguments[z];

arguments represents all the arguments passed to the function. The second argument (aka note1 ) will have the index 1 and so on.

Answer 2

Your problem there is that noteSharp[note1] is using the value of the variable note1 as the key to lookup, whereas noteSharp["note" + z] results in a string of "note" followed by the value of z .

To reference a variable name via a string, use eval :

noteSharp[eval("note" + z)];

However, I would highly recommend not using eval . Others do too , but perhaps there is a counterpoint .

Please do this instead, otherwise Cthulhu might arise...

Pass note1 , note2 , ..., noteN as properties of an object. Therefore you can look up their values exactly as you desire, just one level deeper.

function makeScales(size, notes) {
    var z = 1;
    var note1 = notes["note" + z];
}

// Calling makeScales with our notes.
makeScales(10, {
    note1: 'c',
    note2: 'd',
    note3: 'e',
    // etc.
});