Question

Just when I think I’m getting an understanding of the syntax of Javascript, I run into something like this…

I saw this code on the jqPlot plugin page.

what kind of array is [[]] in javascript? A nested array? I thought I understood the double brackets, but in the commented text, I don’t understand why there is an extra set (question below).

$(document).ready(function(){
// Our data renderer function, returns an array of the form:
// [[[x1, sin(x1)], [x2, sin(x2)], ...]]
var sineRenderer = function() {
var data = [[]];
for (var i=0; i<13; i+=0.5) {
  data[0].push([i, Math.sin(i)]);
}
return data;
};

Why is there an extra set of brackets in this commented statement (the outermost set)?

[[[x1, sin(x1)], [x2, sin(x2)], ...]]

Thanks

Answer 1

Since you are putting in arrays in your data array (which creates arrays inside an array), doing this would avoid that:

var data = [];
for (var i=0; i<13; i+=0.5) {
  data.push([i, Math.sin(i)]);
}

When you use [[]] and then do data[0], you are not utilizing outer array there which jumps in when you output it.