What are the instructions in Vue, and what are their application scenarios in development?

Vue.js is a very popular JavaScript framework. In Vue.js, directives are a very important concept. Directives are a special HTML attribute provided by Vue.js, which can parse expressions in templates. And operate on the DOM. In this article, we will learn about commonly used instructions in Vue and their application scenarios.

1. v-if/v-else-if/v-else

The v-if directive is used to conditionally render elements based on the value of an expression. The element is rendered when the expression evaluates to true. When the expression evaluates to false, the element will not be rendered.

v-else-if and v-else instructions are used to express the "negative condition" of v-if, which means that if the previous v-if instruction fails to check the condition, the following v-else-if or v-else condition.

In development, v-if is often used to control whether a certain element is displayed, such as displaying a login form or user information based on whether the user is logged in. Sample code:

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<div v-if="user.loggedin">
  欢迎回来, {{ user.name }}！
</div>
<div v-else>
  <button @click="showLoginForm">请登录</button>
</div>

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2. v- The show

v-show directive has a similar function to v-if. It can also control whether an element is displayed, but unlike v-if, v-show simply switches the display attribute of CSS.

In development, v-show is usually used to frequently switch the visibility of an element, such as controlling the expansion and closing of a drop-down menu. Sample code:

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<button @click="showMenu=!showMenu">下拉菜单</button>
<ul v-show="showMenu">
  <li>选项1</li>
  <li>选项2</li>
  <li>选项3</li>
</ul>

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3. v- The bind

v-bind directive is used to dynamically bind one or more HTML attributes. The attributes that can be bound include class, style, title, etc. The binding process is two-way. Modifying data in JavaScript can update HTML, and modifying attributes in HTML can update data in JavaScript.

In development, the most commonly used scenario of v-bind is to dynamically bind class and style attributes, such as setting the color and style of buttons according to different states. Sample code:

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<button
  :class="{active: isActive, disabled: isDisabled}"
  :style="{color: textColor, backgroundColor: bgColor}"
  :disabled="isDisabled"
>
  {{ buttonText }}
</button>

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4. v- The for

v-for instruction is used to render elements of an array or object in a loop. It can accept a variable, assign each item of the array or object to this variable in turn, and then render the corresponding element.

In development, v-for is often used for rendering lists and tables, such as rendering news lists, product lists, etc. Sample code:

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<ul>
  <li v-for="(item, index) in list" :key="index">{{ item }}</li>
</ul>

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5. v- The model

v-model directive binds the value of a form input element or custom component to implement two-way data binding. When the value in the form changes, the data in the corresponding Vue instance will also follow. update.

In development, v-model is often used for form implementation, such as two-way data binding of input boxes, radio boxes, check boxes, drop-down boxes and other components. Sample code:

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<input type="text" v-model="message">
<p>{{ message }}</p>

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Six, v- The on

v-on directive is used to bind an event listener, which can listen to various events such as DOM events, custom events, and system events. When the event is triggered, the corresponding method will be called.

In development, v-on is often used to handle user interaction events, such as button clicks, keyboard input, mouse scrolling, etc. Sample code:

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<button @click="incrementCount">{{ count }}</button>

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7. v- The text/v-html

v-text directive is used to set the textContent of the element to the value of the directive. It will only output text in text form and will not parse HTML. The

v-html directive is used to set the element's innerHTML to the value of the directive. HTML tags can be parsed, but there is a risk of XSS.

In development, the v-text/v-html directive should be used with caution because it will increase security risks, so it should only be used to insert some trustworthy content in HTML, such as rendering rich text editors output. Sample code:

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<div v-text="content"></div>
<div v-html="content"></div>

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We introduce in this article It explains the commonly used instructions in Vue and their application scenarios. These instructions are important features of the Vue.js framework, which can effectively improve development efficiency, and also enable Vue.js applications to have richer interactive effects and user experience. Therefore, it is very important to be proficient in these instructions when using the Vue.js framework.

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