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Li Si watched Zhang San’s experiment on slot machines and recorded the winning rate of each slot machine. But Li Si can’t wait too long. When Zhang San finds out the slot machine with the biggest winning rate, he can’t rely on that slot machine to win money. So Li Si came to an end after he felt that he had accumulated enough data.

This page assumes you’ve already read the Components Basics. Read that first if you are new to components.

In 2.6.0, we introduced a new unified syntax (the v-slot directive) for named and scoped slots. It replaces the slot and slot-scope attributes, which are now deprecated, but have not been removed and are still documented here. The rationale for introducing the new syntax is described in this RFC.

Slot Content

Vue implements a content distribution API inspired by the Web Components spec draft, using the <slot> element to serve as distribution outlets for content.

• In this example, a simulated browser-based slot machine game invokes a Lambda function that generates the random results of each slot pull. Those results are returned as the file names of the images that are used to display to the user.
• To install it in the Node.js project, run the following command, $ npm install -save socket.io; JavaScript Client: A standalone build of the client is exposed by default by the server at /socket.io/socket.io.js. Otherwise, it can also be served from any of the CDN providers. To use it from Node.js, install it via this command.
• It is the wild symbol that helps you to form winning combinations on the slots pay lines. The scatter has more than one role on the slot machines. With it, it means ease of access to the bonus rounds as well as additional wins. Gone are the days when you had to dress up and head to the land-based casino to play your favourite slot.

This allows you to compose components like this:

Then in the template for <navigation-link>, you might have:

When the component renders, <slot></slot> will be replaced by “Your Profile”. Slots can contain any template code, including HTML:

Or even other components:

If <navigation-link>‘s template did not contain a <slot> element, any content provided between its opening and closing tag would be discarded.

Compilation Scope

When you want to use data inside a slot, such as in:

That slot has access to the same instance properties (i.e. the same “scope”) as the rest of the template. The slot does not have access to <navigation-link>‘s scope. For example, trying to access url would not work:

As a rule, remember that:

Everything in the parent template is compiled in parent scope; everything in the child template is compiled in the child scope.

Fallback Content

There are cases when it’s useful to specify fallback (i.e. default) content for a slot, to be rendered only when no content is provided. For example, in a <submit-button> component:

We might want the text “Submit” to be rendered inside the <button> most of the time. To make “Submit” the fallback content, we can place it in between the <slot> tags:

Now when we use <submit-button> in a parent component, providing no content for the slot:

will render the fallback content, “Submit”:

But if we provide content:

Then the provided content will be rendered instead:

Named Slots

Updated in 2.6.0+. See here for the deprecated syntax using the slot attribute.

There are times when it’s useful to have multiple slots. For example, in a <base-layout> component with the following template:

For these cases, the <slot> element has a special attribute, name, which can be used to define additional slots:

A <slot> outlet without name implicitly has the name “default”.

To provide content to named slots, we can use the v-slot directive on a <template>, providing the name of the slot as v-slot‘s argument:

Now everything inside the <template> elements will be passed to the corresponding slots. Any content not wrapped in a <template> using v-slot is assumed to be for the default slot.

However, you can still wrap default slot content in a <template> if you wish to be explicit:

Node.js Slot Machines

Either way, the rendered HTML will be:

Note that v-slot can only be added to a <template> (with one exception), unlike the deprecated slot attribute.

Scoped Slots

Updated in 2.6.0+. See here for the deprecated syntax using the slot-scope attribute.

Sometimes, it’s useful for slot content to have access to data only available in the child component. For example, imagine a <current-user> component with the following template:

We might want to replace this fallback content to display the user’s first name, instead of last, like this:

That won’t work, however, because only the <current-user> component has access to the user and the content we’re providing is rendered in the parent.

To make user available to the slot content in the parent, we can bind user as an attribute to the <slot> element:

Attributes bound to a <slot> element are called slot props. Now, in the parent scope, we can use v-slot with a value to define a name for the slot props we’ve been provided:

In this example, we’ve chosen to name the object containing all our slot props slotProps, but you can use any name you like.

Abbreviated Syntax for Lone Default Slots

In cases like above, when only the default slot is provided content, the component’s tags can be used as the slot’s template. This allows us to use v-slot directly on the component:

This can be shortened even further. Just as non-specified content is assumed to be for the default slot, v-slot without an argument is assumed to refer to the default slot:

Note that the abbreviated syntax for default slot cannot be mixed with named slots, as it would lead to scope ambiguity:

Whenever there are multiple slots, use the full <template> based syntax for all slots:

Destructuring Slot Props

Internally, scoped slots work by wrapping your slot content in a function passed a single argument:

That means the value of v-slot can actually accept any valid JavaScript expression that can appear in the argument position of a function definition. So in supported environments (single-file components or modern browsers), you can also use ES2015 destructuring to pull out specific slot props, like so:

This can make the template much cleaner, especially when the slot provides many props. It also opens other possibilities, such as renaming props, e.g. user to person:

You can even define fallbacks, to be used in case a slot prop is undefined:

Dynamic Slot Names

New in 2.6.0+

Dynamic directive arguments also work on v-slot, allowing the definition of dynamic slot names:

Named Slots Shorthand

New in 2.6.0+

Similar to v-on and v-bind, v-slot also has a shorthand, replacing everything before the argument (v-slot:) with the special symbol #. For example, v-slot:header can be rewritten as #header:

However, just as with other directives, the shorthand is only available when an argument is provided. That means the following syntax is invalid:

Instead, you must always specify the name of the slot if you wish to use the shorthand:

Other Examples

Slot props allow us to turn slots into reusable templates that can render different content based on input props. This is most useful when you are designing a reusable component that encapsulates data logic while allowing the consuming parent component to customize part of its layout.

For example, we are implementing a <todo-list> component that contains the layout and filtering logic for a list:

Instead of hard-coding the content for each todo, we can let the parent component take control by making every todo a slot, then binding todo as a slot prop:

Now when we use the <todo-list> component, we can optionally define an alternative <template> for todo items, but with access to data from the child:

However, even this barely scratches the surface of what scoped slots are capable of. For real-life, powerful examples of scoped slot usage, we recommend browsing libraries such as Vue Virtual Scroller, Vue Promised, and Portal Vue.

Deprecated Syntax

The v-slot directive was introduced in Vue 2.6.0, offering an improved, alternative API to the still-supported slot and slot-scope attributes. The full rationale for introducing v-slot is described in this RFC. The slot and slot-scope attributes will continue to be supported in all future 2.x releases, but are officially deprecated and will eventually be removed in Vue 3.

Named Slots with the slot Attribute

Deprecated in 2.6.0+. See here for the new, recommended syntax.

To pass content to named slots from the parent, use the special slot attribute on <template> (using the <base-layout> component described here as example):

Or, the slot attribute can also be used directly on a normal element:

There can still be one unnamed slot, which is the default slot that serves as a catch-all for any unmatched content. In both examples above, the rendered HTML would be:

Scoped Slots with the slot-scope Attribute

Deprecated in 2.6.0+. See here for the new, recommended syntax.

To receive props passed to a slot, the parent component can use <template> with the slot-scope attribute (using the <slot-example> described here as example):

Here, slot-scope declares the received props object as the slotProps variable, and makes it available inside the <template> scope. You can name slotProps anything you like similar to naming function arguments in JavaScript.

Here slot='default' can be omitted as it is implied:

The slot-scope attribute can also be used directly on a non-<template> element (including components):

The value of slot-scope can accept any valid JavaScript expression that can appear in the argument position of a function definition. This means in supported environments (single-file components or modern browsers) you can also use ES2015 destructuring in the expression, like so:

Using the <todo-list> described here as an example, here’s the equivalent usage using slot-scope:

In this paper, we continue to talk about an algorithm of reinforcement learning, called Thompson sampling algorithm. The mathematical basis of this algorithm is Bayesian Inference. Let’s first talk about the basic principles of this algorithm.

Basic Principles of Thompson Sampling Algorithms

We still have the problem of using the old dobby slot machine. As shown in the figure, the horizontal axis represents reward, and the more to the right, the more reward. The three vertical lines represent the average reward for three different slot machines.

Before the algorithm starts, we don’t know anything, so we need to get some basic data. There are four blue data in the picture, which indicate the reward of pressing the blue slot machine. According to these rewards, a mathematical distribution can be obtained. The same green tiger machine can get a distribution, the same as yellow.

These three distributions predict the probability distributions of the mathematical expectations that the three machines give us rewards. Next, based on these three random distributions, we get several random samples and select the machine to get the maximum sample value to press down. However, because it is random, although the actual expectation of yellow is the highest, we may still choose a green data result larger than the Yellow data result.

When we press down, we will get a new observed reward value. When we get a new reward value, we will adjust the distribution of green machines.

Obviously, the green distribution has become higher and narrower. The next steps are the same as here, and the machine with the highest reward value is still selected to press down and continue to adjust the distribution through the results obtained.

When the game goes through many steps, these distributions become very narrow, especially when the basic yellow color matches the actual expectations.

At this time, because we have been choosing the machine with the highest reward value, the probability of pressing yellow will be higher, resulting in yellow will become narrower and narrower, while blue rarely plays, so it is relatively wider.

Thompson sampling algorithm vs. confidence interval upper bound algorithm

We use Thompson sampling algorithm and UCB algorithm to deal with the problem of multi-arm slot machines. Now let’s compare the two algorithms. Take a look at the basic principles of these two algorithms.

Firstly, this UCB algorithm is a deterministic algorithm. When we get the same reward, we make the decision when we decide, so the total revenue and total revenue of each round are deterministic. The decision made in each round is only related to the upper bound of the confidence interval, which is only related to all the observations of the machine. So when the observations of all machines are the same, we will always make the same decision. For Thompson algorithm, it is a stochastic algorithm. One or several steps of Thompson algorithm are controlled by a stochastic function, which is related to luck. It relies on random events, such as when we select points above, although the actual expectation of yellow is greater than that of green, we may still choose data points with green being greater than that of yellow. So it’s a random algorithm.

So for UCB, it also has a feature that it needs to update the upper bound in real time, which can be seen in the previous article when describing the principle of UCB algorithm. For Thompson sampling algorithm, it allows delayed updates or even batch updates. For example, we put a batch of advertisements on the Internet, which allows it to get delayed results. Finally, it is found that Thompson sampling algorithm has better practical application effect than confidence interval algorithm in recent years’practical application and research.

code implementation

First, look at the calculation logic of Thompson sampling algorithm:

The code is directly posted here:

The final total reward is much higher than the previous confidence interval algorithm, and the best advertisement is ad5, so Thompson sampling algorithm is better than the confidence interval algorithm.

Node Js Windows

Above is the basic knowledge of Thompson sampling algorithm in reinforcement learning.