d3.js - check if d3.select or d3.selectAll -

i have method on reusable chart can passed selection , return value if passed d3.select('#id') selection or array of values if passed d3.selectall('.class') selection. i'm interrogating passed argument context._groups[0] instanceof nodelist, feels little fragile using undocumented property, may change in future versions. there more built in way of determining if selection comes select or selectall?

selection.size() not here, tells result of selection, not how called.

edit: here's context of use. i'm using mike bostock's reusable chart pattern , instance includes method getting/setting label donut.

to me, api usage follows principle of least astonishment, it's how expect result returned.

var donut = app.rotatingdonut();  // set label 1 element d3.select('#donut1.donut')     .call(donut.label, 'donut 1')  d3.select('#donut2.donut')     .call(donut.label, 'donut 2')  // set label multiple elements d3.selectall('.donut.group-1')     .call(donut.label, 'group 1 donuts')   // label 1 donut var donutonelabel = d3.select('#donut1').call(donut.label) // donutonelabel === 'donut 1'  // label multiple donuts var donutlables = d3.selectall('.donut').call(donut.label) // donutlabels === ['donut 1', 'donut 2', 'group 1 donuts', 'group 1 donuts'] 

and internal method definition:

app.rotatingdonut = function() {    var label = d3.local();    function donut() {}    donut.label = function(context, value) {     var returnarray;     var islist = context._groups[0] instanceof nodelist;      if (typeof value === 'undefined' ) {        // getter       returnarray = context.nodes()           .map(function (node) {return label.get(node);});        return islist ? returnarray : returnarray[0];     }      // settter     context.each(function() {label.set(this, value);});      // allows method chaining     return donut;   };    return donut } 

well, question here @ s.o. doesn't have answer (it has happened before).

that seems case of question of yours: "is there more built in way of determining if selection comes select or selectall?". no.

to prove that, let's see source code d3.select , d3.selectall (important: not selection.select , selection.selectall, different each other).

first, d3.select:

export default function(selector) {     return typeof selector === "string"         ? new selection([[document.queryselector(selector)]], [document.documentelement])         : new selection([[selector]], root); } 

now, d3.selectall:

export default function(selector) {     return typeof selector === "string"         ? new selection([document.queryselectorall(selector)], [document.documentelement])         : new selection([selector == null ? [] : selector], root); } 

as can see, have two differences here:

1. d3.selectall accepts null. not you.
2. d3.selectall uses queryselectorall, while d3.select uses queryselector.

that second difference 1 suits you, know now, since queryselectorall:

returns list of elements within document (using depth-first pre-order traversal of document's nodes) match specified group of selectors. object returned nodelist. (emphasis mine)

and queryselector only...:

returns first element within document matches specified selector, or group of selectors.

therefore, undocumented (and hacky, since using _groups, not idea) selection._groups[0] instanceof nodelist using right seems way tell selection created d3.select selection created d3.selectall.