Write JavaScript to check domain availability

src/registrar/assets/js/get-gov.js

@@ -1,13 +1,26 @@
+/**
+ * @file get-gov.js includes custom code for the .gov registrar.
+ *
+ * Constants and helper functions are at the top.
+ * Event handlers are in the middle.
+ * Initialization (run-on-load) stuff goes at the bottom.
+ */
+
 /** Strings announced to assistive technology users. */
 var ARIA = {
   QUESTION_REMOVED: "Previous follow-up question removed",
   QUESTION_ADDED: "New follow-up question required"
 }
 
+var DEFAULT_ERROR = "Please check this field for errors.";
+
 var REQUIRED = "required";
 var INPUT = "input";
 
-/** Helper function. Makes an element invisible. */
+// <<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>>
+// Helper functions.
+
+/** Makes an element invisible. */
 function makeHidden(el) {
   el.style.position = "absolute";
   el.style.left = "-100vw";
@@ -18,7 +31,7 @@ function makeHidden(el) {
   el.style.visibility = "hidden";
 }
 
-/** Helper function. Makes visible a perviously hidden element. */
+/** Makes visible a perviously hidden element. */
 function makeVisible(el) {
   el.style.position = "relative";
   el.style.left = "unset";
@@ -33,19 +46,19 @@ function forEachChild(el, selector, func) {
   }
 }
 
-/** Helper function. Removes `required` attribute from input. */
+/** Removes `required` attribute from input. */
 const removeRequired = input => input.removeAttribute(REQUIRED);
 
-/** Helper function. Adds `required` attribute to input. */
+/** Adds `required` attribute to input. */
 const setRequired = input => input.setAttribute(REQUIRED, "");
 
-/** Helper function. Removes `checked` attribute from input. */
+/** Removes `checked` attribute from input. */
 const removeChecked = input => input.checked = false;
 
-/** Helper function. Adds `checked` attribute to input. */
+/** Adds `checked` attribute to input. */
 const setChecked = input => input.checked = true;
 
-/** Helper function. Creates and returns a live region element. */
+/** Creates and returns a live region element. */
 function createLiveRegion(id) {
   const liveRegion = document.createElement("div");
   liveRegion.setAttribute("role", "region");
@@ -64,7 +77,7 @@ var radioToggles = {};
 
 
 /**
- * Helper function. Tracks state of selected radio button.
+ * Tracks state of selected radio button.
  *
  * This is required due to JavaScript not having a native
  * event trigger for "deselect" on radio buttons. Tracking
@@ -75,7 +88,7 @@ function rememberSelected(radioButton) {
   selected[radioButton.name] = radioButton;
 }
 
-/** Helper function. Announces changes to assistive technology users. */
+/** Announces changes to assistive technology users. */
 function announce(id, text) {
   const liveRegion = document.getElementById(id + "-live-region");
   liveRegion.innerHTML = text;
@@ -123,6 +136,70 @@ function revealToggleable(e) {
   }
 }
 
+/**
+ * Slow down event handlers by limiting how frequently they fire.
+ *
+ * A wait period must occur with no activity (activity means "this
+ * debounce function being called") before the handler is invoked.
+ *
+ * @param {Function} handler - any JS function
+ * @param {number} cooldown - the wait period, in milliseconds
+ */
+function debounce(handler, cooldown=600) {
+  let timeout;
+  return function(...args) {
+    const context = this;
+    clearTimeout(timeout);
+    timeout = setTimeout(() => handler.apply(context, args), cooldown);
+  }
+}
+
+/** Asyncronously fetches JSON. No error handling. */
+function fetchJSON(endpoint, callback, url="/api/v1/") {
+    const xhr = new XMLHttpRequest();
+    xhr.open('GET', url + endpoint);
+    xhr.send();
+    xhr.onload = function() {
+      if (xhr.status != 200) return;
+      callback(JSON.parse(xhr.response));
+    };
+    // nothing, don't care
+    // xhr.onerror = function() { };
+}
+
+/** Modifies CSS and HTML when an input is valid/invalid. */
+function toggleInputValidity(el, valid, msg=DEFAULT_ERROR) {
+  if (valid) {
+    el.setCustomValidity("");
+    el.removeAttribute("aria-invalid");
+    el.classList.remove('usa-input--error');
+  } else {
+    el.classList.remove('usa-input--success');
+    el.setAttribute("aria-invalid", "true");
+    el.setCustomValidity(msg);
+    // this is here for testing: in actual use, we might not want to
+    // visually display these errors until the user tries to submit
+    el.classList.add('usa-input--error');
+  }
+}
+
+function _checkDomainAvailability(e) {
+  const callback = (response) => {
+    toggleInputValidity(e.target, (response && response.available));
+    if (e.target.validity.valid) {
+      e.target.classList.add('usa-input--success');
+      // do other stuff, like display a toast?
+    }
+  }
+  fetchJSON(`available/${e.target.value}`, callback);
+}
+
+/** Call the API to see if the domain is good. */
+const checkDomainAvailability = debounce(_checkDomainAvailability);
+
+// <<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>>
+// Event handlers.
+
 /** On radio button selection change, handles associated toggleables. */
 function handleToggle(e) {
   // hide any previously visible HTML associated with previously selected radio buttons
@@ -131,6 +208,39 @@ function handleToggle(e) {
   revealToggleable(e);
 }
 
+/** On input change, handles running any associated validators. */
+function handleInputValidation(e) {
+  const attribute = e.target.getAttribute("validate") || "";
+  if (!attribute.length) return;
+  const validators = attribute.split(" ");
+  let isInvalid = false;
+  for (const validator of validators) {
+    switch (validator) {
+      case "domain":
+        checkDomainAvailability(e);
+        break;
+    }
+  }
+  toggleInputValidity(e.target, !isInvalid);
+}
+
+// <<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>><<>>
+// Initialization code.
+
+/**
+ * An IIFE that will attach validators to inputs.
+ *
+ * It looks for elements with `validate="<type> <type>"` and adds
+ * change handlers for each known type.
+ */
+ (function validatorsInit() {
+  "use strict";
+  const needsValidation = document.querySelectorAll('[validate]');
+  for(const input of needsValidation) {
+    input.addEventListener('input', handleInputValidation);
+  }
+})();
+
 /**
  * An IIFE that will hide any elements with `hide-on-load` attribute.
  *

src/registrar/templates/application_contact.html

@@ -23,7 +23,7 @@ of a larger entity. If so, enter information about your part of the larger entit
 
   <fieldset class="usa-fieldset">
     {{ wizard.form.street_address|add_label_class:"usa-label" }}
-    {{ wizard.form.street_address|add_class:"usa-input" }}
+    {{ wizard.form.street_address|add_class:"usa-input"|attr:"validate:domain" }}
   </fieldset>
 
   {% if wizard.steps.prev %}