Trying to understand better how data contexts works in Meteor, as I can't figure out this problem I'm facing. Haven't found a clear answer anywhere. I have the following templates
<template name="list">
{{#each listItem}}
{{> listItemDetail}}
{{/each}}
</template>
<template name="listItemDetail">
<p>{{_id}} {{title}}</p>
<p>{{idViaHelper}}</p>
</template>
And in my Javascript I have
Template.list.helpers({
'listItem': () => {
return List.find().fetch();
})
Template.listItemDetail.helpers({
'idViaHelper': () => {
return this._id
})
As far as my understanding of data contexts within Meteor goes, using #each sets the context for each instance of the listItemDetail template to be a document that that is returned from the listItem helper.
And this works as I'd expect when it comes to using {{_id}} in the listItemDetail template, showing the ID of the document.
But if I try to get the same _id via a helper {{idViaHelper}} which uses this._id, I get undefined. When I try console.log(this), it shows me that this is referring to the Window object. But I have no idea why. What is going on and why does the data context not get picked up in the template helper?
This is my first post, thanks for your help!
You are right about the Meteor datacontext flow.
What you are doing is working.
You only forget what the this represent into a lambda function.
Read the the part Lexical this from MDN, it's better explained than what I could say: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions
For your case, the easier way to get the datacontext directly from your this on helpers is to pass by usual anonymous function.
Just try:
Template.listItemDetail.helpers({
'idViaHelper': function(){
return this._id
})
That's it.
You've got unlucky on this one, there is no issue related to Meteor here.
Other related question you could find useful: meteor helper functions, lambdas and lexical this
Julien Leray is correct in his answer regarding lexical this. You lose the data context when using lambda expressions. However, Meteor offers you ways to access your Template data without lexical this, viz.:
Template.list.helpers({
'listItem': () => List.find().fetch();
});
Template.listItemDetail.helpers({
'idViaHelper': () => Template.currentData()._id
});
You can use both Template.currentData() and Template.instance().data.
Also, note that if you have a lambda expression that only includes a single return statement, you can use the shortcut syntax as I did above.
// ECMAScript 5
var myFunc = function (a, b, c) {
return b * a - c;
};
Becomes:
// ECMAScript 6
const myFunc = (a, b, c) => b * a - c;
Related
Does Ember have any template helper "get-value-with-key"
I found the below usage, but not sure what it does exactly ?
{{get-value-with-key item optionValuePath}}
There is an Ember Get Helper for HTMLBars.
You might have to install the Package "ember-get-helper" if you are on ember < 2.1.
{{get object key}}
Let's say you have the following object:
var obj = {
"key1": {
"subkey1": "hello world"
}
}
Using Ember 3.18, to access "hello world" from the template, you can do:
{{get obj 'key1.subkey1'}}
You can use the build-in get helper. See docs here: Ember Docs.
Usage example:
{{get object key}}
Note that the get helper will not be able to work on all JavaScript keys. For example, a key with a '.' will not work with the built-in get helper.
For example, if you have a valid JavaScript object like:
const example = {
'example.pdf': 'pdf_url'
}
// You can access this key normally via
example['example.pdf']
however, this will not work in the get helper
{{get this.example 'example.pdf'}}
One solution is to create a helper that can support the types of keys you need to support. For example, I made a helper that can work on keys with a '.' by including '.' in the key name which are escaped like with ''.
{{get this.example 'example\.pdf'}}
The ember twiddle can be found here: twiddle
Other Helpful Sources:
Dot notation for object keys with dots in the name
How do I reference a field name that contains a dot in mustache template?
I just want to run the template string against an object and examine the result
I have a string that is a template. I've "compiled" it. Now I want to run it against an object and examine the result.
But this doesn't work:
var template = '<div>{{#each items}}<div>{{item}}</div>{{/each}}</div>';
var compiled = Ember.Handlebars.compile(template);
var result = compiled({ items: [1, 2, 3] }); // ERRORS
What I want to get is the DOM result of running my compiled string against an object. In other words, a set of DOM elements that looks something like this:
<div>
<div>1</div>
<div>2</div>
<div>3</div>
</div>
It appears that Ember.Handlebars.compile is very tightly coupled to other parts of an Ember application, to the point it expects a lot of things to be populated in the context I'm passing ot the compiled function. I have yet to figure out what all of these things are, or if there is a better way to create a context to pass to the compiled function.
Other things:
I don't want to use plain "non-Ember" Handlebars.
I'd like to avoid creating an Ember Application if I can.
I don't really want to answer questions about "why" I want to do this. This is what I want to do. :P
Why do you want to do this? ;)
Honestly the easiest way to do this will be to create a view. Ember hooks up a bunch of fancy rendering stuff when it calls compile due to the data binding etc, so it's difficult to create it straight from the compile function (it passes in a slew of additional stuff, like buffers etc...)
var view = Ember.View.extend({
template:Ember.Handlebars.compile('hello <div>{{#each item in view.items}}<div>{{item}}</div>{{/each}}</div>')
});
var foo = view.create({ items: [1, 2, 3] });
foo.appendTo('#blah');
Example
http://emberjs.jsbin.com/qeyenuyi/1/edit
// you must wait for all bindings to sync before you can check the contents of #blah:
var empty = $('#blah').html(); // this will be empty
Ember.run.next(function(){
var notEmpty = $('#blah').html(); // this will have the proper result in it
});
or you can hook up to the didInsertElement callback
var foo = view.create(blah);
foo.didInsertElement = function(){
console.log(foo.$().html());
}
foo.appendTo('#blah');
http://emberjs.jsbin.com/qeyenuyi/6/edit
The bindings are still in tact when you create a Ember handlebars template, so you can modify the object passed in and it will update the template.
http://emberjs.jsbin.com/qeyenuyi/2/edit
On Github, many Handlebars helpers are presented. You can find them here.
I'd like to use them, but have no Idea, how to include them. The code is looking as it's javascript (files are ending with .js ...), but words like 'import','export','default' are confusing me.
As I understand (guess), I have to include the if-condition.js at first. Later, the other (included) files refer to this file.
But when I do this, the console throws an Error:
Uncaught SyntaxError: Unexpected reserved word .
Has anyone an idea, how to get these codes working?
import and export are keywords for the upcoming module syntax in the next version of Javascript. You can use them today by using a transpiler to convert it to normal ES5 syntax.
However, if you're only using a few helpers, it's very easy to 'transpile' them by hand. Instead of exporting the function, just pass it to a Ember.Hanldebars.registerBoundHelper call. Here's the if-condition helper:
Ember.Handlebars.registerBoundHelper('if-condition', function() {
var args = [].slice.call(arguments);
var options = args.pop();
var context = (options.contexts && options.contexts[0]) || this;
if (!options.conditional) {
throw new Error("A conditional callback must be specified when using the if-condition helper");
}
// Gather all bound property names to pass in order to observe them
var properties = options.types.reduce(function(results, type, index) {
if (type === 'ID') {
results.push(args[index]);
}
return results;
}, []);
// Resolve actual values for all params to pass to the conditional callback
var normalizer = function() {
return Ember.Handlebars.resolveParams(context, args, options);
};
// This effectively makes the helper a bound helper
// NOTE: 'content' path is used so that multiple properties can be bound to using the `childProperties` argument,
// however this means that it can only be used with a controller that proxies values to the 'content' property
return Ember.Handlebars.bind.call(context, 'content', options, true, options.conditional, normalizer, properties);
});
So let's say I'm storing <div>{{name}}</div> and <div>{{age}}</div> in my database.
Then I want to take the first HTML string and render it in a template - {{> template1}} which just renders the first string with the {{name}} handlebar in it. Then I want to give that newly generated template/html data, so that it can fill in the handlebar with the actual name from the database, so that we would get <div>John</div>. I've tried doing
<template name="firstTemplate">
{{#with dataGetter}}
{{> template1}}
{{/with}}
</template>
Where template1 is defined as
<template name="template1">
{{{templateInfo}}}
</template>
And templateInfo is the helper that returns the aforementioned html string with the handlebar in it from the database.
dataGetter is just this (just an example, I'm working with differently named collections)
Template.firstTemplate.dataGetter = function() {
return Users.findOne({_id: Session.get("userID")});
}
I can't get the {{name}} to populate. I've tried it a couple of different ways, but it seems like Meteor doesn't understand that the handlebars in the string need to be evaluated with the data. I'm on 0.7.0 so no Blaze, I can't upgrade at the moment due to the other packages I'm using, they just don't have 0.8+ version support as of yet. Any ideas on how I can get this to work are much appreciated.
In 1.0 none of the methods described above work. I got this to work with the function below defined in the client code. The key was to pass the options { isTemplate: true} to the compile function.
var compileTemplate = function(name, html_text) {
try {
var compiled = SpacebarsCompiler.compile(html_text, { isTemplate:true });
var renderer = eval(compiled);
console.log('redered:',renderer);
//Template[name] = new Template(name,renderer);
UI.Template.__define__(name, renderer);
} catch (err){
console.log('Error compiling template:' + html_text);
console.log(err.message);
}
};
The you can call with something like this on the client:
compileTemplate('faceplate', '<span>Hello!!!!!!{{_id}}</span>');
This will render with a UI dynamic in your html
{{> Template.dynamic template='faceplate'}}
You can actually compile strings to templates yourself using the spacebars compiler.. You just have to use meteor add spacebars-compiler to add it to your project.
In projects using 0.8.x
var compiled = Spacebars.compile("<div>{{name}}</div> and <div>{{age}}</div>");
var rendered = eval(compiled);
Template["dynamicTemplate"] = UI.Component.extend({
kind: "dynamicTemplate",
render: rendered
});
In projects using 0.9.x
var compiled = SpacebarsCompiler.compile("<div>{{name}}</div> and <div>{{age}}</div>");
var renderer = eval(compiled);
Template["dynamicTemplate"] = Template.__create__("Template.dynamicTemplate", rendered);
Following #user3354036's answer :
var compileTemplate = function(name, html_text) {
try {
var compiled = SpacebarsCompiler.compile(html_text, { isTemplate:true }),
renderer = eval(compiled);
console.log('redered:',renderer);
//Template[name] = new Template(name,renderer);
UI.Template.__define__(name, renderer);
} catch (err) {
console.log('Error compiling template:' + html_text);
console.log(err.message);
}
};
1) Add this in your HTML
{{> Template.dynamic template=template}}
2) Call the compileTemplate method.
compileTemplate('faceplate', '<span>Hello!!!!!!{{_id}}</span>');
Session.set('templateName','faceplate');
Save the template name in a Session variable. The importance of this is explained in the next point.
3) Write a helper function to return the template name. I have used Session variable to do so. This is important if you are adding the dynamic content on a click event or if the parent template has already been rendered. Otherwise you will never see the dynamic template getting rendered.
'template' : function() {
return Session.get('templateName');
}
4) Write this is the rendered method of the parent template. This is to reset the Session variable.
Session.set('templateName','');
This worked for me. Hope it helps someone.
If you need to dynamically compile complex templates, I would suggest Kelly's answer.
Otherwise, you have two options:
Create every template variation, then dynamically choose the right template:
eg, create your templates
<template name="displayName">{{name}}</template>
<template name="displayAge">{{age}}</template>
And then include them dynamically with
{{> Template.dynamic template=templateName}}
Where templateName is a helper that returns "age" or "name"
If your templates are simple, just perform the substitution yourself. You can use Spacebars.SafeString to return HTML.
function simpleTemplate(template, values){
return template.replace(/{{\w+}}/g, function(sub) {
var p = sub.substr(2,sub.length-4);
if(values[p] != null) { return _.escape(values[p]); }
else { return ""; }
})
}
Template.template1.helpers({
templateInfo: function(){
// In this context this/self refers to the "user" data
var templateText = getTemplateString();
return Spacebars.SafeString(
simpleTemplate(templateText, this)
);
}
Luckily, the solution to this entire problem and any other problems like it has been provided to the Meteor API in the form of the Blaze package, which is the core Meteor package that makes reactive templates possible. If you take a look at the linked documentation, the Blaze package provides a long list of functions that allow for a wide range of solutions for programmatically creating, rendering, and removing both reactive and non-reactive content.
In order to solve the above described problem, you would need to do the following things:
First, anticipate the different HTML chunks that would need to be dynamically rendered for the application. In this case, these chunks would be <div>{{name}}</div> and <div>{{age}}</div>, but they could really be anything that is valid HTML (although it is not yet part of the public API, in the future developers will have more options for defining this content in a more dynamic way, as mentioned here in the documentation). You would put these into small template definitions like so:
<template name="nameDiv">
<div>{{name}}</div>
</template>
and
<template name="ageDiv">
<div>{{age}}</div>
</template>
Second, the definition for the firstTemplate template would need to be altered to contain an HTML node that can be referenced programmatically, like so:
<template name="firstTemplate">
<div></div>
</template>
You would then need to have logic defined for your firstTemplate template that takes advantage of some of the functions provided by the Blaze package, namely Blaze.With, Blaze.render, and Blaze.remove (although you could alter the following logic and take advantage of the Blaze.renderWithData function instead; it is all based on your personal preference for how you want to define your logic - I only provide one possible solution below for the sake of explanation).
Template.firstTemplate.onRendered(function() {
var dataContext = Template.currentData();
var unrenderedView = Blaze.With(dataContext, function() {
// Define some logic to determine if name/age template should be rendered
// Return either Template.nameDiv or Template.ageDiv
});
var currentTemplate = Template.instance();
var renderedView = Blaze.render(unrenderedView, currentTemplate.firstNode);
currentTemplate.renderedView = renderedView;
});
Template.firstTemplate.onDestroyed(function() {
var renderedView = Template.instance().renderedView;
Blaze.remove(renderedView);
});
So what we are doing here in the onRendered function for your firstTemplate template is dynamically determining which of the pieces of data that we want to render onto the page (either name or age in your case) and using the Blaze.With() function to create an unrendered view of that template using the data context of the firstTemplate template. Then, we select the firstTemplate template element node that we want the dynamically generated content to be contained in and pass both objects into the Meteor.render() function, which renders the unrendered view onto the page with the specified element node as the parent node of the rendered content.
If you read the details for the Blaze.render() function, you will see that this rendered content will remain reactive until the rendered view is removed using the Blaze.remove() function, or the specified parent node is removed from the DOM. In my example above, I am taking the reference to the rendered view that I received from the call to Blaze.render() and saving it directly on the template object. I do this so that when the template itself is destroyed, I can manually remove the rendered view in the onDestroyed() callback function and be assured that it is truly destroyed.
A very simple way is to include in the onRendered event a call to the global Blaze object.
Blaze.renderWithData(Template[template_name], data ,document.getElementById(template_id))
I have a viewmodel whose template I want to change dynamically at runtime when the state of my application changes. I referred to this link
while coming up with my solution.
In my html page I have a div that is bound to a list of view models:
<div class="app"
data-bind="template: {name: templateSelector, foreach: viewModelBackStack}">
</div>
And my templateSelector method looks like this:
this.templateSelector = function(viewModel)
{
if (!_itemTemplate)
{
_itemTemplate = ko.computed(function() {return this.template();}, viewModel);
}
return _itemTemplate();
}
var _itemTemplate;
As can be seen, I am constructing a computed observable which returns viewModel's template.
My viewModel looks like this:
function MyViewModel
{
this.template = ko.observable("MyTemplate");
}
I am changing the value of template as a result of an ajax call being completed and I see that computed observable is called correctly as well (I placed an alert in there to verify it), however the bindings in html does not update the template of my viewmodel. Any help will be appreciated.
UPDATE: I found the bug that was causing it not to work. Basically I was including jquery.tmpl plugin before including knockout.js. Removing jquery.tmpl did the trick !
I don't see a problem with your code, unless it lies in the part where you update the template observable as the result of an AJAX call. Make sure that you have a reference to your view model and are setting it as an observable vm.template(newValue); and not recreating the observable.
Here is your code working: http://jsbin.com/ipijet/5/edit#javascript,html,live
One thing to note is that bindings are already executed within the context of a computed observable, so it is unnecessary to create your own within your templateSelector function.
You can simply create a function that returns your observable directly like:
this.getTemplate = function(data) {
return data.template();
};
http://jsbin.com/ipijet/3/edit#javascript,html,live
Here is an article that I wrote a while back on this topic: http://www.knockmeout.net/2011/03/quick-tip-dynamically-changing.html