source: node_modules/d3-transition/src/transition/delay.js

import {get, init} from "./schedule.js";

function delayFunction(id, value) {
  return function() {
    init(this, id).delay = +value.apply(this, arguments);
  };
}

function delayConstant(id, value) {
  return value = +value, function() {
    init(this, id).delay = value;
  };
}

export default function(value) {
  var id = this._id;

  return arguments.length
      ? this.each((typeof value === "function"
          ? delayFunction
          : delayConstant)(id, value))
      : get(this.node(), id).delay;
}