[英]The context of “this” in Meteor template event handlers (using Handlebars for templating)
A quick question on the context of the event handlers for templates in Meteor (with Handlebars). 关于Meteor中模板事件处理程序(带Handlebars)的上下文的快速问题。
Well, this is only partially true. 嗯,这只是部分正确。 Let's use an example from the docs: 让我们使用文档中的示例:
<template name="scores">
{{#each player}}
{{> playerScore}}
{{/each}}
</template>
<template name="playerScore">
<div>{{name}}: {{score}}
<span class="givePoints">Give points</span>
</div>
</template
Template.playerScore.events({
'click .givePoints': function () {
Users.update({_id: this._id}, {$inc: {score: 2}});
});
Here the "this" context of the 'click .givePoints' event handler is indeed the template instance of playerScore. 这里'click .givePoints'事件处理程序的“this”上下文确实是playerScore的模板实例。 Let's modify the html: 我们来修改html:
<template name="scores">
<span class="click-me">Y U NO click me?<span>
{{#each player}}
{{> playerScore}}
{{/each}}
</template>
<template name="playerScore">
<div>{{name}}: {{score}}
<span class="givePoints">Give points</span>
</div>
</template>
... and add an event handler for .click-me on the scores template: ...并在分数模板上为.click-me添加事件处理程序:
Template.scores.events({
'click .click-me': function () {
console.log(this);
}
});
Now, if you click the span, what do you get logged? 现在,如果单击跨度,您会记录什么? The Window object! Window对象! What did I expect to get? 我期望得到什么? The template object! 模板对象! Or maybe the data context, but it's neither. 或者也许是数据上下文,但它们都不是。 However, inside the callbacks (eg Template.scores.rendered = function(){ ... }) the context of "this" is always the template instance. 但是,在回调内部(例如Template.scores.rendered = function(){...}),“this”的上下文始终是模板实例。
I guess my real question would be: is this something to do with 我想我真正的问题是:这是否与此有关
Thanks! 谢谢!
This video explains the concepts: 该视频解释了这些概念:
http://www.eventedmind.com/posts/meteor-spark-data-annotation-and-data-contexts . http://www.eventedmind.com/posts/meteor-spark-data-annotation-and-data-contexts 。
The direct answer to your question: 直接回答你的问题:
The thisArg inside an event handler should point to a data context. 事件处理程序中的thisArg 应指向数据上下文。 But sometimes the data context is undefined
. 但有时数据上下文是undefined
。 When you use the Function.prototype.call(thisArg, ...)
in JavaScript, if the thisArg is undefined (eg a dataContext is undefined) the browser will set this
equal to window. 当您使用Function.prototype.call(thisArg, ...)
在JavaScript中,如果thisArg是不确定的(例如,一个DataContext是不确定的),浏览器会设置this
等于窗口。 So, the docs aren't wrong per se but the event handling code isn't guarding against the possibility of a data context being undefined. 因此,文档本身并没有错 ,但事件处理代码无法防止数据上下文未定义的可能性。 I'm guessing that will be fixed in short order. 我猜这将在短期内修复。
So, what produces a data context for a template? 那么,什么产生模板的数据上下文? Normally your root template won't even have a data context. 通常,您的根模板甚至不具有数据上下文。 In other words, the Template function is called without an object. 换句话说,在没有对象的情况下调用Template函数。 But if you use the {{#with
block helper or the {{#each
iterator, a data context will be created for each item in the list, or in the case of the with helper, the object. 但是如果使用{{#with
块帮助器或{{#each
迭代器,将为列表中的每个项创建数据上下文,或者对于with helper,则为对象。
Example: 例:
var context = {};
<template name="withHelper">
{{#with context}}
// data context is the context object
{{/with}}
</template>
var list = [ {name: "one"}, {name: "two"} ];
<template name="list">
{{#each list}}
{{ > listItem }} // data context set to the list item object
{{/each}}
</template>
The first parameter in the function is the event. 函数中的第一个参数是事件。 So you could use the target of the event to grab your element. 因此,您可以使用事件的目标来获取元素。
Template.scores.events({
'click .click-me': function (event, template) {
console.log(event.target);
$(event.target).text("O but I did!");
}
});
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