Meteor模板事件处理程序中“this”的上下文(使用Handlebars进行模板化)

时间:2021-10-26 16:35:01

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的上下文(带Handlebars)的快速问题。

  • In the section of Documentation on template instances (http://docs.meteor.com/#template_inst) it is mentioned that "Template instance objects are found as the value of this in the created, rendered, and destroyed template callbacks and as an argument to event handlers"
  • 在关于模板实例的文档部分(http://docs.meteor.com/#template_inst)中,提到“在创建,呈现和销毁的模板回调中找到模板实例对象作为其值,并作为事件处理程序的参数“
  • In the Templates section (http://docs.meteor.com/#templates) it says "Finally, you can use an events declaration on a template function to set up a table of event handlers. The format is documented at Event Maps. The this argument to the event handler will be the data context of the element that triggered the event."
  • 在“模板”部分(http://docs.meteor.com/#templates)中,它说“最后,您可以在模板函数上使用事件声明来设置事件处理程序表。格式记录在事件映射中。事件处理程序的this参数将是触发事件的元素的数据上下文。“

Well, this is only partially true. Let's use an example from the docs:

嗯,这只是部分正确。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. Let's modify the html:

这里'click .givePoints'事件处理程序的“this”上下文确实是playerScore的模板实例。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:

...并在分数模板上添加.click-me的事件处理程序:

Template.scores.events({
  'click .click-me': function () {
    console.log(this);
  }
});

Now, if you click the span, what do you get logged? The Window object! What did I expect to get? The template object! Or maybe the data context, but it's neither. However, inside the callbacks (e.g. Template.scores.rendered = function(){ ... }) the context of "this" is always the template instance.

现在,如果单击跨度,您会记录什么? Window对象!我期望得到什么?模板对象!或者也许是数据上下文,但它们都不是。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

  • a bug in Handlebars, Meteor or somewhere in between?
  • Handlebars,Meteor或介于两者之间的错误?
  • slightly incomplete documentation on the templates?
  • 关于模板的文档略有不完整?
  • me completely misinterpreting the docs or not understanding something fundamental about Meteor or Handlebars?
  • 我完全误解了文档或者没有理解Meteor或Handlebars的基本内容?

Thanks!

谢谢!

2 个解决方案

#1


27  

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. But sometimes the data context is undefined. When you use the Function.prototype.call(thisArg, ...) in JavaScript, if the thisArg is undefined (e.g. a dataContext is undefined) the browser will set this equal to window. 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. I'm guessing that will be fixed in short order.

事件处理程序中的thisArg应指向数据上下文。但有时数据上下文是不确定的。当您在JavaScript中使用Function.prototype.call(thisArg,...)时,如果未定义thisArg(例如,未定义dataContext),浏览器将其设置为等于window。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。我猜这将在短期内修复。

So, what produces a data context for a template? Normally your root template won't even have a data context. In other words, the Template function is called without an object. 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.

那么,什么产生模板的数据上下文?通常,您的根模板甚至不会有数据上下文。换句话说,在没有对象的情况下调用Template函数。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>

#2


13  

The first parameter in the function is the event. So you could use the target of the event to grab your element.

函数中的第一个参数是事件。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!");
  }
});

#1


27  

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. But sometimes the data context is undefined. When you use the Function.prototype.call(thisArg, ...) in JavaScript, if the thisArg is undefined (e.g. a dataContext is undefined) the browser will set this equal to window. 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. I'm guessing that will be fixed in short order.

事件处理程序中的thisArg应指向数据上下文。但有时数据上下文是不确定的。当您在JavaScript中使用Function.prototype.call(thisArg,...)时,如果未定义thisArg(例如,未定义dataContext),浏览器将其设置为等于window。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。我猜这将在短期内修复。

So, what produces a data context for a template? Normally your root template won't even have a data context. In other words, the Template function is called without an object. 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.

那么,什么产生模板的数据上下文?通常,您的根模板甚至不会有数据上下文。换句话说,在没有对象的情况下调用Template函数。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>

#2


13  

The first parameter in the function is the event. So you could use the target of the event to grab your element.

函数中的第一个参数是事件。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!");
  }
});