Prevent HTML Page Refresh - html

Question

At this stage I'm mostly used to backend Javascript and server side Java, so my HTML is not as savvy as it needs to be.
I've built several applications that require user input with Apps script, but I was using the now deprecated UI service, as I'm not a designer and this provided an easy way to design simple pages to pass data back and forth. With the UI service having been deprecated for some time, I'm begging the arduous task of migrating these services to the HTML service, and I'm noticing some difference in behavior.
For example, when submitting a form, the entire page refreshes to a blank page, and I can't seem to prevent that. The UI service would remain static for information re-entry, and I can't find a working method to get the HTML service to either stop refreshing or reload the form.
Simple code to reproduce my issue:
function doGet() {
return HtmlService.createHtmlOutputFromFile('test')
.setSandboxMode(HtmlService.SandboxMode.IFRAME);
}
function logValues(value){
Logger.log('Something worked....');
}
With the index file being:
<form>
<input type="submit" value="Book Meeting" onclick="google.script.run
.logValues()">
</form>
Some things I've tried:
1) Adding a callback to the 'doGet' function, to attempt to get the page to load again.
2) Adding a whole new function to try and call a NEW HTML page.
The issue here is my poor understanding of the HTML service, but is there a simple way for me to just clear the form for re-submission, or alternatively just reload the page? None of the other questions I've found on SO adequately answer this question in a way I can understand.

Answer 1

Since you're technically submitting your form by clicking the submit button, then that creates the page refresh. You need to cancel the submit event with the preventDefault function, which "Cancels the event if it is cancelable, without stopping further propagation of the event."
See the docs here: https://developer.mozilla.org/en-US/docs/Web/API/Event/preventDefault
So maybe you can try something along these lines (straight from the docs):
function stopDefAction(evt) {
evt.preventDefault();
}
document.getElementById('my-checkbox').addEventListener('click', stopDefAction, false);
Another option is to remove the form/input elements and simply use a button element instead, which doesn't trigger a page refresh on click.

Answer 2

It's an interesting ride switching old UI services across, I just did that with one of my applications and it has really improved the readability of the code. I posted a copy of a basic version of what I was doing in another question
Once you get your head around it all it becomes a lot simpler. This is a really basic example of using multiple HTML files similar to your example using the HTMLService when submitting forms (you can pass in parameters instead)
Code.gs
function doGet() {
return HtmlService.createTemplateFromFile('Main')
.evaluate()
.setSandboxMode(HtmlService.SandboxMode.NATIVE);
}
function onLogin(form) {
if (form.username == "fuzzyjulz") {
var template = HtmlService.createTemplateFromFile('Response');
//Setup any variables that should be used in the page
template.firstName = "Fuzzy";
template.username = form.username;
return template.evaluate()
.setSandboxMode(HtmlService.SandboxMode.NATIVE)
.getContent();
} else {
throw "You could not be found in the database please try again.";
}
}
function include(filename) {
return HtmlService.createTemplateFromFile(filename)
.evaluate()
.setSandboxMode(HtmlService.SandboxMode.IFRAME)
.getContent();
}
Main.html
<?!= include('CSS'); ?>
<script>
function loadPage(htmlOut) {
var div = document.getElementById('content');
div.innerHTML = htmlOut;
document.getElementById('errors').innerHTML = "";
}
function onFailure(error) {
var errors = document.getElementById('errors');
errors.innerHTML = error.message;
}
</script>
<div id="errors"></div>
<div id="content">
<?!= include('Login'); ?>
</div>
CSS.html
<style>
p b {
width: 100px;
display: inline-block;
}
</style>
Login.html
<script>
function onLoginFailure(error) {
var loginBtn = document.getElementById('loginBtn');
loginBtn.disabled = false;
loginBtn.value = 'Login';
onFailure(error);
}
</script>
<div class="loginPanel">
<form>
<p>
<b>Username: </b>
<input type="text" name="username"/>
</p>
<input type="button" id="loginBtn" value="Login" onclick="this.disabled = true; this.value = 'Loading...';google.script.run
.withSuccessHandler(loadPage)
.withFailureHandler(onLoginFailure)
.onLogin(this.parentNode)"/>
</form>
</div>
Response.html
<div class="text">
Hi <?= firstName ?>,<br/>
Thanks for logging in as <?= username ?>
</div>