input.js

import {observe} from "./observe.js";

export function input(input) {
  return observe(function(change) {
    var event = eventof(input), value = valueof(input);
    function inputted() { change(valueof(input)); }
    input.addEventListener(event, inputted);
    if (value !== undefined) change(value);
    return function() { input.removeEventListener(event, inputted); };
  });
}

function valueof(input) {
  switch (input.type) {
    case "range":
    case "number": return input.valueAsNumber;
    case "date": return input.valueAsDate;
    case "checkbox": return input.checked;
    case "file": return input.multiple ? input.files : input.files[0];
    case "select-multiple": return Array.from(input.selectedOptions, o => o.value);
    default: return input.value;
  }
}

function eventof(input) {
  switch (input.type) {
    case "button":
    case "submit":
    case "checkbox": return "click";
    case "file": return "change";
    default: return "input";
  }
}