会话

¥Session

Meteor 客户端会话 API 的文档。

¥Documentation of Meteor's client-side session API.

Session 在客户端上提供了一个全局对象，你可以使用它来存储任意一组键值对。使用它来存储列表中当前选定的项目等内容。

¥Session provides a global object on the client that you can use to store an arbitrary set of key-value pairs. Use it to store things like the currently selected item in a list.

Session 的特殊之处在于它是反应式的。如果你从模板内部调用 Session.get('currentList')，则每当调用 Session.set('currentList', x) 时，模板都会自动重新渲染。

¥What's special about Session is that it's reactive. If you call Session.get('currentList') from inside a template, the template will automatically be rerendered whenever Session.set('currentList', x) is called.

要将 Session 添加到你的应用，请在你的终端中运行此命令：

¥To add Session to your application, run this command in your terminal:

meteor add session

Session.set

Client only

Summary:

Set a variable in the session. Notify any listeners that the value has changed (eg: redraw templates, and rerun any Tracker.autorun computations, that called Session.get on this key.)

Arguments:

Source code

Name	Type	Description	Required
key	String	The key to set, eg, selectedItem	Yes
value	EJSONable or undefined	The new value for key	Yes

import { Session } from 'meteor/session';
import { Tracker } from 'meteor/tracker';
import { Meteor } from 'meteor/meteor';

Tracker.autorun(() => {
  Meteor.subscribe('chatHistory', { room: Session.get('currentRoomId') });
});

// Causes the function passed to `Tracker.autorun` to be rerun, so that the
// 'chatHistory' subscription is moved to the room 'home'.
Session.set('currentRoomId', 'home');

Session.set 也可以使用键和值的对象来调用，这相当于在每个键/值对上单独调用 Session.set。

¥Session.set can also be called with an object of keys and values, which is equivalent to calling Session.set individually on each key/value pair.

Session.set({
  a: 'foo',
  b: 'bar'
});

Session.setDefault

Client only

Summary:

Set a variable in the session if it hasn't been set before. Otherwise works exactly the same as Session.set.

Arguments:

Source code

Name	Type	Description	Required
key	String	The key to set, eg, selectedItem	Yes
value	EJSONable or undefined	The new value for key	Yes

import { Session } from "meteor/session";


const result = Session.setDefault();
  "key",
 { num:  42 , someProp:  "foo" },
);

这在初始化代码中很有用，可以避免每次加载新版本的应用时都重新初始化会话变量。

¥This is useful in initialization code, to avoid re-initializing a session variable every time a new version of your app is loaded.

Session.get

Client only

Summary:

Get the value of a session variable. If inside a reactive computation, invalidate the computation the next time the value of the variable is changed by Session.set. This returns a clone of the session value, so if it's an object or an array, mutating the returned value has no effect on the value stored in the session.

Arguments:

Source code

Name	Type	Description	Required
key	String	The name of the session variable to return	Yes

Blaze.js 中的此示例

¥This example in Blaze.js

main.html

<template name="main">
  <p>We've always been at war with {{theEnemy}}.</p>
</template>

main.js

Template.main.helpers({
  theEnemy() {
    return Session.get('enemy');
  }
});

Session.set('enemy', 'Eastasia');
// Page will say "We've always been at war with Eastasia"

Session.set('enemy', 'Eurasia');
// Page will change to say "We've always been at war with Eurasia"

Session.equals

Client only

Summary:

Test if a session variable is equal to a value. If inside a reactive computation, invalidate the computation the next time the variable changes to or from the value.

Arguments:

Source code

Name	Type	Description	Required
key	String	The name of the session variable to test	Yes
value	String, Number, Boolean, null or undefined	The value to test against	Yes

import { Session } from "meteor/session";


const result = Session.equals();
  "key",
  "value",
);

如果值是标量，则这两个表达式执行相同的操作：

¥If value is a scalar, then these two expressions do the same thing:

Session.get('key') === value
Session.equals('key', value)

...但第二个总是更好。它会触发更少的无效（模板重绘），从而使你的程序更高效。

¥...but the second one is always better. It triggers fewer invalidations (template redraws), making your program more efficient.

Blaze.js 中的此示例：

¥This example in Blaze.js:

main.html

<template name="postsView">
  {{#each posts}}
    {{> postItem}}
  {{/each}}
</template>

<template name="postItem">
  <div class="{{postClass}}">{{title}}</div>
</template>

main.js

Template.postsView.helpers({
  posts() {
    return Posts.find();
  }
});

Template.postItem.helpers({
  postClass() {
    return Session.equals('selectedPost', this._id)
      ? 'selected'
      : '';
  }
});

Template.postItem.events({
  'click'() {
    Session.set('selectedPost', this._id);
  }
});

此处使用 Session.equals 意味着当用户单击某个项目并更改选择时，只会重新渲染新选择的项目和新取消选择的项目。

¥Using Session.equals here means that when the user clicks on an item and changes the selection, only the newly selected and the newly unselected items are re-rendered.

如果使用了 Session.get 而不是 Session.equals，那么当选择发生变化时，所有项目都会重新渲染。

¥If Session.get had been used instead of Session.equals, then when the selection changed, all the items would be re-rendered.

对于对象和数组会话值，你不能使用 Session.equals；相反，你需要使用 underscore 软件包并写入 _.isEqual(Session.get(key), value)。

¥For object and array session values, you cannot use Session.equals; instead, you need to use the underscore package and write _.isEqual(Session.get(key), value).