Develop Reference

How to use getElementById with a reactive var and Meteor

In general doing a getElementById works pretty well like this :
console.log(document.getElementById('{{chart_id}}').setAttribute("id", "div_top2"));
But it returns me null and I don't really know why but I think it's becoming from the following lines:
<template name="chart">
<div id="{{chart_id}}"></div>
</template>
And later in the JS I do :
Template.currentData().chart_id
to get the div and place a HighChart here.
The thing I want to do is to rename the id (by the way I want to add a identifier so the final id would be something like <div id ="{{chart_id}}+ a random number">)
Then I could do this in my JavaScript:
Template.currentData().chart_id + theRandomNumber

Finally I have modified the HTML where I create the <div> and it looks like this :
{{#each gimmeContainersToCreateChart}}
{{> chart chart_id=this._id}}
<!-- {{> chart chart_id="cpuChart"}}
{{> chart chart_id="netChart"}}
{{> chart chart_id="diskChart"}} -->
{{/each}}
gimmeContainersToCreateChartreturns a cursor with the running&&paused containers from the collection

How to dynamically populate iron-list elements

So I have an iron-list element for a user's data history. The iron-list is not part of a custom element. It is simply on the page. I want to populate once the user has successfully logged in. Perhaps it is just my inexperience with polymer, but there doesn't seem to be a straightforward way to do this. First attempt (simplified for reading, e.g. I don't actually use jquery, there's lots of error-handling code I'm omitting, etc):
<iron-list as="item" style='height: 100%;' id='history-list'>
<template>
<div style='min-height: 140px;'>
<ul>
<!-- various fields for each record as list items -->
</ul>
</div>
</template>
</iron-list>
<script>
//once user is logged in
var items = $.getJSON('userhistoryscript');
//setAttribute doesn't work either
document.getElementById('history-list').items = items;
</script>
I would swear this worked in an earlier version of Polymer. But it doesn't seem to work now, which is fine, but I need an alternative.
Some alternatives I've considered:
Have iron-ajax element in same DOM scope and set '
the URL once the user is logged in to trigger the
xhr request. I'm not sure whether or not that'd work.
Wrap the list in a custom element and use an
iron-meta-query per chrisW's answer.
Those options are terrible. I cannot believe there is no simpler way to accomplish this feat. How do I conditionally fetch data based on user input and dynamically add an iron-list to the page (or update one that's already there)? Is there really no API for this use case?
UPDATE
Thank you for your answers. Turns out that my original code actually works fine: it was actually a build process issue. For some reason iron-list did not get installed when I installed the project dependencies through bower. I took out the vulcanized import (which must not have contained a ref to iron-list either) and imported all the elements directly, then I got the 404 and figured out what had happened.

I think that for best practices, you should use this.$.historyList to refeer id on this element. Anyway, when you get data to populate iron-listyou should use this.set('items', data); An example using your element looks like:
<iron-list>
<template is="dom-repeat" items="{{data}}" as="history">
<!--history.property-->
</template>
</iron-list>
<script>
Polymer({
properties:{
data:{type:Array, value:[],}
},
_functionToSetDataWhenUserIsLoggedIn: function(data){
this.set('data',data);
}
});
</script>
Edit
An example of iron-list
<template is="dom-bind">
<iron-ajax url="data.json" last-response="{{data}}" auto></iron-ajax>
<iron-list items="[[data]]" as="item">
<template>
<div>
Name: <span>[[item.name]]</span>
</div>
</template>
</iron-list>
</template>
This example is using an ajax call that executes automatically and populates the iron-listwithout the need to create a customized element.
More about iron-list on:
https://elements.polymer-project.org/elements/iron-list

I didn't entirely understand your question. Hope this helps.
<iron-list items="[[data]]" as="item">
<template>
<div>
Name: <span>[[item.name]]</span>
</div>
</template>
</iron-list>
properties:{
data:{type:Array, value:[],}
},
// the attached function is automatically called
attached: function() {
// Use an iron meta in the element that you keep track in of login information
// or create an onLogin listener
var isLoggedIn = new Polymer.IronMetaQuery({key: 'isLoggedIn'}).value,
if (isLoggedIn) {
var jsonData = $.getJSON('userhistoryscript');
this.set('data',jsonData);
}
}
Side note, when access elements by ids in Polymer elements, make sure you do it this way:
this.$.elementId
or
Polymer.dom('#elementId')
Edit since you don't want to create a custom polymer element
Source Code
<template is="dom-bind">
<iron-list id="list">
</iron-list>
</template>
<script>
document.addEventListener('onLogin', function(event) {
var list = document.getElementById('#list');
var jsonDataObjects = $.getJSON('userhistoryscript');
for (var i = 0; i < jsonDataObjects.length; i++) {
var div = document.createElement('div');
div.textContent = jsonDataObjects[i].info; // change this line
list.appendChild(div);
}
});
</script>

How to execute a callback after an #each is done?

I'm having trouble with a callback after the #each has finished. I have a template named "content":
<template name="content">
{{#if Template.subscriptionsReady}}
{{#each currentData}}
<div data-cid="{{this._id}}"></div>
{{/each}}
{{else}}
Loading...
{{/if}}
</template>
At first I wait for a subscription, when this is available, I iterate through my Collection with {{#each}} and append the div. What I need is a sort of callback for when the for-each loop is done (in other words DOM ready).
Template.content.onRendered()
-> triggers to early
I also tried appending an image after the {{each}} and fire a function in its onload like this:
<img style="height:0;width:0" src="*mysource*" onload="callback()">
-> did work sometimes but not reliable somehow
Is there a way to get this callback? I do not fear to change the structure of this template, if that brings the solution.

There's no easy way to get notified when a Spacebars {{#each}} block has done rendering into the DOM every item getting iterated over.
The best solution is to use another reactive computation (Tracker.autorun) to observe your (reactive) current data.
Everytime your current data (which is likely a cursor) is modified, you can run arbitrary code after every other reactive computations are done performing whatever their job is, using Tracker.afterFlush.
The {{#each}} block is one of those computations, whose role is to listen to the reactive data source you give it as argument and rerender its Template.contentBlock as many times as items fetched from the source being iterated over, with the current item as current data context.
By listening to the exact same reactive data source as the {{#each}} block helper and running your code AFTER it has finished its own reactive computation, you can get the actual requested behavior without relying on some weird tricks.
Here is the full implementation of this pattern :
JS
Template.content.helpers({
currentData: function(){
return Template.currentData();
}
});
Template.content.onRendered(function(){
this.autorun(function(){
var cursor = Template.currentData();
// we need to register a dependency on the number of documents returned by the
// cursor to actually make this computation rerun everytime the count is altered
var count = cursor.count();
//
Tracker.afterFlush(function(){
// assert that every items have been rendered
console.log(this.$("[data-cid]") == count);
}.bind(this));
}.bind(this));
});

I had a similar problem and after a lot of searching found the following solution. I tried using Tracker, onRendered and other tricks, none of them worked. This could be considered more of a hack, but works. Unfortunately can't remember where I found this solution initially.
Start with your template, but add an template tag after your each.
<template name="content">
{{#if Template.subscriptionsReady}}
{{#each currentData}}
<div data-cid="{{this._id}}"></div>
{{/each}}
{{doneTrigger}}
{{else}}
Loading...
{{/if}}
</template>
Then define a helper that returns null.
Template.content.helpers({
doneTrigger: function() {
Meteor.defer(function() {
// do what you need to do
});
return null;
}
});
You can read more about Meteor.defer() here, but it is equivalent to using a 0 millisecond setTimeout.

You can also use sub-templates and count the number of sub-templates rendered. If this number is the number of items in the collection, then all are rendered.
<template name="content">
{{#if Template.subscriptionsReady}}
{{#each currentData}}
{{> showData}}
{{/each}}
{{else}}
Loading...
{{/if}}
</template>
<template name="currentData">
<div data-cid="{{this._id}}"></div>
</template>
With that, initialize a reactive variable and track it:
var renderedCount = new ReactiveVar(0);
Tracker.autorun(function checkIfAllRendered() {
if(renderedCount.get() === currentData.count() && renderedCount.get() !== 0) {
//allDataRendered();
}
});
When the currentData template is rendered, increment it, and decrement it when it is destroyed.
Template.currentData.onRendered(function() {
renderedCount.set(++renderedCount.curValue);
});
Template.currentData.onDestroyed(function() {
renderedCount.set(--renderedCount.curValue);
});

A possibly simpler approach to consider - create a template around your #each block and then get an onRendered event afterwards:
html:
<template name="content">
{{#if Template.subscriptionsReady}}
{{> eachBlock}}
{{else}}
Loading...
{{/if}}
</template>
<template name="eachBlock">
{{#each currentData}}
<div data-cid="{{this._id}}"></div>
{{/each}}
</template>
js:
Template.eachBlock.onRendered(function(){
console.log("My each block should now be fully rendered!");
});

Polymer 1.0 - Issue with displaying values inside template is="dom-repeat"

While migrating to Polymer 1.0 from 0.5 I have come across an interesting thing. Thought it might help others having similar problem.
I have an element where I am using <template is="dom-repeat" items="{{customers}}">...</template>. The problem I am facing is I have to place every single property binding inside a HTML element. The code below what I intended to write:
<template is="dom-repeat" items="{{customers}}">
<div>
{{item.name}}<br />
{{item.addr}}, {{item.addr2}}<br />
{{item.phone}}
</div>
</template>
But it is only displaying the value for {{item.name}}. The reason is other property bindings are not wrapped within separate HTML tags, they are not displaying at all!
I tried the following but didn't work either:
<template is="dom-repeat" items="{{customers}}">
<div>
<p>{{item.name}}</p>
<span>{{item.addr}} {{item.addr2}}</span>
</div>
</template>
Means, I put {{item.name}} inside a <p>...</p> tag and placed {{item.addr}} and {{item.addr2}} inside a single <span>...</span> tag.
Then I went on and put every single property binding wrapped by their own HTML tags like the following:
<template is="dom-repeat" items="{{customers}}">
<div>
<p>{{item.name}}</p>
<span style="display:block">{{item.addr}}, <span>{{item.addr2}}</span></span>
<span style="display:block;">{{item.phone}}</span>
</div>
</template>
and it works!!
I truly have no idea whether it is a bug of 1.0 or there is something I am doing wrong! If anybody knows the answer please help.
Thanks in advance

You're not doing anything wrong. With the introduction of Polymer 0.9 (and later 1.0) data-binding to the content of text nodes only works if you wrap everything into its own element.
See the Polymer documentation:
The binding annotation must currently span the entire content of the tag
So you have to remove all whitespace and other characters for it to work.
Example from the documentation:
<!-- this works -->
<template>
First: <span>{{first}}</span><br>
Last: <span>{{last}}</span>
</template>
<!-- Not currently supported! -->
<div>First: {{first}}</div>
<div>Last: {{last}}</div>
<!-- Not currently supported! -->
<div>
{{title}}
</div>
Edit
As of Polymer 1.2, the issue described in the question is no longer problematic / erroneous. Compound bindings now work, see release notes on the Polymer blog.

Just a heads up, for element attributes though you can use something like a helper function for string concatenation. Here's an example.
<my-foo fullname="{{computeFullName(firstname, lastname)}}">
Hi, my name is <span>{{firstname}}</span>.
</my-foo>
...
computeFullName: function(first, last) {
return first + ' ' + last;
}
And here's the link: https://www.polymer-project.org/1.0/docs/migration.html#data-binding
EDIT:
For node content as well, string concatenation can be done using computed properties (I call them helper functions). Here's an example,
<dom-module id="x-custom">
<template>
My name is <span>{{fullName}}</span>
</template>
</dom-module>
<script>
Polymer({
is: 'x-custom',
properties: {
first: String,
last: String,
fullName: {
type: String,
// when `first` or `last` changes `computeFullName` is called once
// (asynchronously) and the value it returns is stored as `fullName`
computed: 'computeFullName(first, last)'
}
},
computeFullName: function(first, last) {
return first + ' ' + last;
}
...
});
</script>

With Polymer 1.2 you example code will actually work. Binding annotations no longer need to span the entire tag.
Example:
<div>first name: [[name.first]] last name: [[name.last]]</div>
https://blog.polymer-project.org/releases/2015/11/02/release-1.2.0/

You'll want to use a computed property to combine values. Search for them on this page https://www.polymer-project.org/1.0/docs/devguide/properties.html

Polymer - dynamic template rendering

is it somehow possible to render the template in a polymer element dynamically at runtime or when some light-dom elements are available?
I have the following situation:
index.html
<mega-menu>
<span class="menuTriggerText">Open Menu</span>
<ul class="test">
<li>TEST1</li>
<li>TEST2</li>
</ul>
<ul class="test">
<li>TEST1</li>
<li>TEST2</li>
</ul>
</mega-menu>
in my polymer-element.html i want to do something as follows:
<template>
<template repeat="{{temp}}"><p>I want to try this</template>
</template>
Polymer('mega-menu, {
created:function(){},
ready: function(){
//getting markup from light-dom
this.temp = document.getElementsByClassName('test');
},
attached:function(){},
detached: function(){},
attributeChanged: function(attrName, oldVal, newVal){}
});
Now, my question is - how do i get this to work? do i need to bind something on my template? or do i need some kind of event-listener or observer on something?
Thanks, Gbeschbacher

This is precisely what content insertion points are for. You can select top-level light DOM markup to render at specific locations in the Shadow DOM. <content select=""></content> takes a CSS selector and grabs nodes from the light DOM.
Your example would be:
<polymer-element name="mega-menu" noscript>
<template>
<content select=".test"></content>
</template>
</polymer-element>
You should not need to pry into the light DOM like this for such a simple case, but for the sake of completeness, we can get your example working with a few important tweaks:
document.getElementsByClassName('test') looks for nodes in the entire document. This is not what you want. You only want children of <mega-menu>. Instead of document use this (e.g. this.querySelectorAll('.test')).
You're giving <template repeat="{{temp}}"> a NodeList. It won't be able to stamp that out. It expects an Array. Something like this.temp = [].slice.call(this.querySelectorAll('.test')); would work.
http://jsbin.com/balodowi/2/edit