There is some misunderstanding here: you're confusing d3.csv, which is a request, with d3.csvParse, which parses a string (and also mixing D3 v3 syntax with D3 v4 syntax). This is the difference:

d3.csv (D3 v4)

The d3.csv function, which takes as arguments (url[[, row], callback]):

Returns a new request for the CSV file at the specified url with the default mime type text/csv. (emphasis mine)

So, as you can see, you use d3.csv when you want to request a given CSV file at a given url.

For example, the snippet below gets the CSV at the url between quotes, which looks like this...

name, parent

Level 2: A, Top Level

Top Level, null

Son of A, Level 2: A

Daughter of A, Level 2: A

Level 2: B, Top Level

... and logs the parsed CSV file, check it:

d3.csv(https://gist.githubusercontent.com/d3noob/fa0f16e271cb191ae85f/raw/bf896176236341f56a55b36c8fc40e32c73051ad/treedata.csv, function(data){

    console.log(data);

});

<script src=https://d3js.org/d3.v4.min.js></script>

d3.csvParse

On the other hand, d3.csvParse (or d3.csv.parse in D3 v3), which takes as arguments (string[, row]):

Parses the specified string, which must be in the delimiter-separated values format with the appropriate delimiter, returning an array of objects representing the parsed rows.

So, you use d3.csvParse when you want to parse a string.

Here is a demo, suppose you have this string:

var data = foo,bar,bazn42,33,42n12,76,54n13,42,17;

If you want to parse it, you'll use d3.csvParse, not d3.csv:

var data = foo,bar,bazn42,33,42n12,76,54n13,42,17;



var parsed = d3.csvParse(data);



console.log(parsed);

<script src=https://d3js.org/d3.v4.min.js></script>