d3js：d3.csv，它的数据消失了

Question

I use this code:

var map_json; // in global scope
var map;
...
function get_data() {
   map_json = d3.json("data/russia_1e_7sr.json", function (e, d) {
      map = d;
   });
   // ... draw map
}

If I debug this code then I see the result. If I close debugger and then refresh the page, the results disappears.

I suggest that something happening with object's memory. But what?

What is the right way to get data with d3? Yes, I see an examples such this:

d3.csv("file.csv", function(e,d) {
   // ... use d
   // all things processed inside this function
}

What if I want to load several data parts from different sources?

Answer 1

You need to shift the draw map bit:

var map_json; // in global scope

...
function get_data() {
   map_json = d3.json("data/russia_1e_7sr.json", function (e, d) {
       var map;= d;
       // ... draw map
   });
}

map won't be populated yet where you have it.