In d3.js the csvParse function works like:
d3.csvParse("foo,bar\n1,2\n2,3");
// [{foo: "1", bar: "2"}, {foo: "2", bar:"3"}, columns: ["foo", "bar"]]
Q1: What the structure name of the returned data? especially the "columns" properties?
Outside d3.js, if I do
var data = [{foo: "1", bar: "2"}, {foo: "2", bar:"3"}, columns: ["foo", "bar"]]
//uncaught syntaxerror unexpected token ':'
Q2: Why is the error? How to get around?
The output you're seeing is just a regular JavaScript array and columns is simply a property of that array. In JavaScript, arrays can have properties.
If you have a look at the source code, you'll see this:
var rows = []
And then:
rows.columns = columns || [];
Here is a very basic example:
const arr = [1, 2, 3, 4, 5];
arr.columns = "foo";
console.log(arr)Look at your browser's console (not the snippet one), you'll see this (in Chrome and Firefox, but not in Safari):
[1, 2, 3, 4, 5, columns: "foo"]
Regarding your error...
//uncaught syntaxerror unexpected token ':'
... have in mind that that is just the output in the console, that is not a valid array literal notation.
Q1: The columns: ["foo","bar"] makes an error. You can't assign the attribute columns if its not inside an object. What you can do instead is { columns: ["foo","bar"] }, which will crwate an object with the columns.