Is the usage of eval() justified here?

Question

The JavaScript object data has an attribute 'amplitudes' which is a string concatenated bunch of bitmask arrays coming from the server.

var data = {
  "amplitudes":           
  "[1,1,1,4,1,1],[1,1,1,1,1,1],[1,1,4,1,9,1],[1,1,9,1,16,1],[1,32,1,1,1,9],[4,4,4,1,1,1]"
}

.

This needs be broken down into six independant arrays. I am using a combination of split() and eval() to accomplish it in the following way:

var amplitudes = [];
amplitudes = data.amplitudes.split("],[");
for(var i=0;i<amplitudes.length;i+=1){
    (i+1)%2>0 ? amplitudes[i] = amplitudes[i] + "]" : amplitudes[i] = "[" + amplitudes[i];
    amplitudes[i] = eval(amplitudes[i]);
}

Questions

---

1) Is there a more elegant and efficient way to do this?? I am not too happy with the usage of eval(), but had a feeling split is more efficient than a regex? I haven't run a benchmark yet.

2) I am also open to manipulating the format in which the field 'amplitudes' is stored in database so that my overall design gets simpler.

Suggestions welcome

Answer 1

As you probably process your data with a server-side language simply make it generate a JavaScript array. If you have an array in your server-side code, use a JSON encoder to build the JavaScript object/array.

var data = {
  "amplitudes": [[1,1,1,4,1,1], [1,1,1,1,1,1], [1,1,4,1,9,1], [1,1,9,1,16,1], [1,32,1,1,1,9], [4,4,4,1,1,1]]
}

If you cannot change what you get from the server, you can do it using eval but in a much simpler way:

var str = "[1,1,1,4,1,1],[1,1,1,1,1,1],[1,1,4,1,9,1],[1,1,9,1,16,1],[1,32,1,1,1,9],[4,4,4,1,1,1]";
var arr = eval('[' + str + ']');

Answer 2

If you can change the server, just have the "amplitudes" property be an array of arrays, and don't write it out with quotes:

var data = {
  amplitudes: [ [1, 1, 1, 4, 1, 1 ], [ 1, 1, 1, 1, 1, 1 ], ... ]
};

Now your client need do no decoding at all.