Is there a way to schedule an event when a key is pressed on the keyboard. I can't seem to find that in the event triggers.
There are two possible answers to this.
First one is that slate is just javascript, with sandboxing layers (for security and functionality) so to an extent if you know the dom element ID could just try to reach it with something similar to this: https://developer.mozilla.org/en-US/docs/Web/API/Document/keypress_event#examples
const log = document.getElementById('log');
document.addEventListener('keypress', logKey);
function logKey(e) {
log.textContent += ` ${e.code}`;
}
Due to the sandboxing layers it may not be possible depending on what you are trying to achieve. If you want to do this natively, then the trick to effectively designing apps with slate is to think that the whole world gets recomputed whenever a variable changes. Similar to what happens with the lifecycle refreshes on Angular.js
There isn't a native global event for a key press in slate, so if you want to listen for any keypress that bubbles to the document, that won't work. But for most use cases you can work around it. For example by setting a variable from an input and then just read it from somewhere else.
1 - Go to the variables tab and create a new variable.
2 - Create an input box.
3 - Set the variable to update every time the variable changes.
4 - Read the variable from some widget or function.
I am very new to JavaScript and Polymer. I do like the PWA concept but now hit some roadblocks.
I tried to use polymerfire <firebase-auth> and was able to do google provider logins. But got blocked as I don't know how to do Facebook provider login and didn't find anywhere on how to use the tag as I wish to provide Facebook login too in JavaScript. If someone guides me to a source that works I will then not need part 2 of the question.
So, I tried facebook login via Graph API FB.login(). FB.login() has callback and I was not able to extract the response.name, public_profile and set it to Polymer attribute say {{user}} like
var userName = response.name; and then this.user = {displayName : userName};
I noticed that as soon as I exit FB.login() callback on successful login, I lose the changes done in assignment in callback to 'this.user ' object.
My question is - I am not able to make two way binding work in polymer. How can I change the object in child element and then it propagates to all the pages / polymer elements?
How can I change the object in child element and then it propagates to all the pages / polymer elements?
Well really that depends on how you set up all the pages. If you're in the parent, you can pass functions, variables, and objects to the child element by passing it in the component.
<ChildElement details={{_details}}/> // If you want to pass a details object to the child
<ChildElement sqft={{square(size)}}/> // This will call the square function inside your ChildElement and pass in the parameter size
Use the latter to call a function in your child and that function will have access to all the elements within that scope.
If you're in the child and you want to change something in the parent, you can do a callback with this.fire(someFunction()), and then create a function in your parent that with the same name. It's not too bad when you're just passing from parent to child or vice versa but if you're passing it everywhere, then you might want to look into some sort of state management. Passing things from one place to everywhere else will get ugly real fast.
When I google "Knockout Google Maps" I find quite some KO-based Google Maps implementations. All of which I was able to find take the approach to use a custom binding handler whereas I originally intended to implement it as a Knockout component.
Examples:
http://www.codeproject.com/Articles/351298/KnockoutJS-and-Google-Maps-binding
http://www.hoonzis.com/knockoutjs-and-google-maps-binding/
https://github.com/manuel-guilbault/knockout.google.maps
Can anyone point me in the right direction why one would prefer a custom binding handler over a KO component here?
My planned use case is this:
I'm implementing a page with a list of address search results. The list so far is a KO component, each list entry is generated by another KO component which the list component repeatedly calls in a foreach binding. Next to this list of search results I need a google map showing the result entries also in the map. There will also be quite a lot of interaction between the list, the list entries and the map.
Here's what I've got so far:
var GMap = function () {
var self = this;
var initMap = function() {
var map = new google.maps.Map(document.getElementById('map'), {
zoom: 13,
center: {lat: 51.4387974, lng: 6.9922915}
});
};
initMap();
};
$(document).ready(function() {
ko.components.register('gmap', {
viewModel: GMap,
template: { element: 'gmap' }
});
ko.applyBindings();
});
#map {
height: 400px;
width: 600px;
}
<script src="https://maps.googleapis.com/maps/api/js?v=3.22"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.0/knockout-min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<gmap></gmap>
<template id="gmap">
<div id="map"></div>
</template>
A component and a custom handler are completely different things.
Custom binding
Basically a custom binding have access to:
the HTML component where it's used
the bound value (expression supplied to the binding)
all the other bindings in the element
the binding context of the element, from which you can acces to $root, $parent, and so on
Its definition includes two functions:
init: that allows to do the initial setup, like initializing widgets, setting event handlers and so on
update: it's called after init. In that moment you can access properties (including observable properties) through the binding, all the element bindings, the context and so on. This creates subscriptios that will call update when any of the accessed observable changes.
So a custom binding shuld be used when you need to interact directly with the DOM element, for example to modify its properties, initialize widgets, subscribe to events and so on
Component
A component is completely different. When you define a componente you must define:
a template, which is a set of DOM elements, usually with bindings
a viewmodel (usually a constructor or a factory)
When you use the component:
the viewmodel is instanced
the template is loaded
the viewmodel is bound to the template
So, a componente allows to reuse viewmodels and templates
So, what's the difference?
A custom binding has direct access to the DOM elements, allowing to interact with them, subscribe to events, modify properties, and so on
A component is only a viewmodel, and a set of DOM elements with bindings to that particular viewmodel.
So, in the case of Google Maps, which needs to initialize a widget (the map) and interact with Map events, and respond to observable propèrties cahnges, you could never use a component, because the component doesn't allow the direct interaction with the DOM elements. (Remember is a bunch of HTML elements with bindings, and the corrresponding view model, whic can't include any logic to intercat with those elements).
A custom binding usually applies to a single element (althoug it could handle its children, like foreach). In the case of Google Maps you only need the element in which you'll show the map.
A component is usually a more or less complex set of DOM elements, which are not accesible "from the outside". The only communication with the main viewmodel is done through parameters. The component cannot directly interact with the DOM elements: it must do it via ko bindings.
So, for the case of Google Maps is clear that you need a custom binding.
It only makes sense to create a component when you want to modularize or reuse a set of DOM elements, and the related viewmodel, which can also include functionality like accessing web services (via AJAX), making computations (propbaly by using computed observables), and so on. For example, a shopping cart could be implemented using a component, which would include:
the DOM elements to show the items in the cart (probably an HTML table, and some controls)
controls to modify the cart content (for example for deleting elements, or changing quantities)
a viewmodel that show the total, the taxes and so on
functionality to store the cart for later, or pay for it (which could be ajax calls to services)
In this case the cart would have a viewmodel which would include the computed observables (to show the total and taxes), the functionality to remove items, or modify quantities, or store or pay, and so on. And a concrete set of DOM elements with bindings for this viewmodel, i.e. the HTML to show the cart and interact with it.
In the case of Google Maps a component could not be used without the help of a custom binding or with the hacky use of additional, non ko, scripts.
If you wanted to show a list of places beside a map, and modify that list, you could use a component, which would include a viewmodel with the list and related functionality, and a template including an element with the Google Maps custom binding. That would make sense: viewmodel + several elements.
Conclusion
This all means that a custom binding usually have a deep interaction with the bound DOM element, while a component has a higher level interaction with the elements, which must be done through bindings.
So, they play a role at a very different level. You cannot compare or interchange them.
If you insist on doing so, you could create a beast of a binding which behaves like a component, becasue you have full control on the elements, and full acces to the view model, but that's harder to implement than a component. And probably could do the other way round also in some esoteric way.
Binding
Binding, a custom or not, is a very simple concept that covers 2 things:
A property of a UI element changes, and thus it should update an object (ViewModel)
A property of the object (ViewModel) changes, and thus it should update the UI element.
From the above if only 1 implemented, it is called One Way Binding (because if you change the UI, it will update the object but not the other way around). If both 1 and 2 are implemented, it is called Two Way Binding.
So at any time if you think you need something to do that, you would need to use binding, custom binding if the framework does not have the binding you need.
Most likely, the maps you speak of needed something like above. And it actually did because the author says this in the first paragraph:
Concretely, you can learn how to make the maps marker part of the View and automatically change its position any time when the ViewModel behind changes.
See, the author talks about 2 above: When the ViewModel changes, change the position of UI element.
Component
A component is a concept of having a reusable item that may have a UI but not necessarily, and all the code needed to make it work packaged along with it. This way it can be reused. For example, it may simply be an input UI element that only allows numbers. All the code needed for it is packaged along with the UI element.
Now the code packaged along with it may code related to bindings. It may even have custom bindings if the framework they used did not have the binding they needed. In addition it may have additional code that has nothing to do with binding.
Furthermore, a component may have a single UI element or multiple. A good example of a component with multiple elements would be a message box.
In Conclusion
Bindings and Components are separate things. A component may have bindings within it or it may have other code to make it work or both.
In the case of the maps you speak of, they have only added a feature to it: To react to changes in the ViewModel. It is not a component because it is not self contained and reusable.
They could have done it using a component. However, if they did that and said it is a KO component, it may still have KO specific binding code packaged with it along with the ViewModel and all the UI elements needed.
I can get my <iron-meta> instance to work properly when using a static value. But when I bind the value to a dynamic variable (using {{}}) it <iron-meta> no longer behaves as expected.
Does <iron-meta> support binding its value to dynamic variables?
<iron-meta id="meta" key="info" value="foo/bar"></iron-meta> // works
<iron-meta id="meta" key="info" value="{{str}}"></iron-meta> // fails
Previous work
This question is a refinement of this question in order to clarify that the ONLY thing causing the problem is the change from a static string value to a dynamic string value binding. I was getting a lot of other suggesting that had nothing to do with the change from static to dynamic so I thought it might be best to rewrite the question to clarify that. But the entire code context is contained in the links there if that would help.
Alternative solutions
There has been some recent chatter about using <iron-localstorage>. Perhaps that is the best way to go for dynamic binding essentially creating global variables?
Yes, <iron-meta> does support binding to variables, but perhaps not in the way you think.
Example: http://plnkr.co/edit/QdNepDrg9b3eCTWF6oRO?p=preview
I looked through your code here, here, and here but I'm not entirely clear what your expectations are. Hopefully my attached repro might shed some light. I see you have declaratively bound <iron-meta id="meta" key="route" xvalue="foo-bar" value="{{route}}"></iron-meta> which is fine - when route changes, iron-meta's key="route" will update accordingly.
However, be aware that in Polymer 1.0, <iron-meta> is in essence a one-way bind from parent to child in the sense that you set a meta key value dynamically by binding to a property; but to get that value, you'll have to get it imperatively via iron-meta's byKey() method.
<iron-meta> is just a simple monostate pattern implementation without an in-built path notification mechanism. What this means is value changes do not propagate upwards. Therefore, doing something like
<!-- this does not work like the way you think -->
<iron-meta id="meta" key="foo" value="{{bar}}">
in order to get the value of foo, or listen to changes to foo, does not work. This behaves more like a setter, where you set the value of foo based on your data-bound property bar.
From what I gather, it seems that you're trying to implement some sort of global variable functionality. A monostate implementation used to work in Polymer 0.5, but not in 1.0. Unfortunately, until Google endorses a "best-practice" pattern for this, suggestions till-date seems a bit speculative to me. You might find this (Polymer 1.0 Global Variables) helpful.
I have had success using <iron-signals> to communicate global information. I know there is a warning in the <iron-signals> documentation that discourages its use for related elements, but when broadcasting a shared resource it seems just the thing. For example:
// source element
var db = SomeDB.init();
this.fire('iron-signal', { name: 'database', data: db });
<-- sink element -->
<iron-signals on-iron-signal-database="dbChange"></iron-signals>
class SinkElement {
dbChange(e, detail) {
this.db = detail;
this.db.getSomeData();
}
}
Update: here are the docs for this situation: Conditional templates use the if attribute to conditionally create a template instance.
this app, plnkr.co, should do the following:
use core-ajax component to get project_location from DB(JSON in this example)
use google-map component to display the map with marker
when user drags the market, use core-ajax to save the new location to DB
Q: How to make google-map component to wait with it's rendering until AJAX request is finished?
Currently this error is appearing:
"Exception caught during observer callback: TypeError: latitude must be a number", and I assume that is because google-map is rendered before {{project_location}} is initiated.
<core-ajax id="ajax_get_location"
auto
url="project_location.json"
params='{"idProject":"{{idProject}}"}'
on-core-response="{{locationLoaded}}"
handleAs="json"
response = "{{project_location}}"></core-ajax>
<google-map id="project_location_map"
zoom="{{project_location.location_map_zoom}}"
fitToMarkers>
<google-map-marker
latitude ="{{project_location.location_map_marker_latitude | toFixed(2)}}"
longitude ="{{project_location.location_map_marker_longitude | toFixed(2)}}"
title ="{{project_title}}"
draggable ="true"
>
{{project_title}}
</google-map-marker></google-map>
I think the cleanest approach is not to think about this as a timing issue with <core-ajax>. Fundamentally, the problem is that you don't want to include the <google-map> element on your page until there's a value for project_location. In your snippet, the project_location value comes from <core-ajax>, but you could easily imagine a different implementation in which project_location is populated via some other means.
So, if you think about it that way, what would make sense is to wrap the <google-map> in a conditional template that checks for a value of project_location:
<template if="{{project_location}}">
<google-map>
...
</google-map>
<template>
You can change a value on the model when core-axax has finished and wrap the other elements with a <template if="{{ajaxHasFinished}}">...</templ<te>
Besides what others have said, an another way is demonstrated in the tutorial https://www.polymer-project.org/docs/start/tutorial/step-3.html, in which you create another element to do the ajax thing, and use it in your original element. The data transfer is achieved through attributes and data binding.
I think it's a better way because you separate the data display with data fetching, making it look better in software engineering.
P.S. I've tried what other answers said, but I found out it didn't matter whether you use if condition or not.