select box placeholder

下拉框的占位符可以通过设置`<option>`标签的`disabled`和`selected`属性来实现，如下所示：

<select>
  <option disabled selected value="">请选择</option>
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
</select>

其中，设置`disabled`属性表示该选项不可选，设置`selected`属性表示默认选中该选项，`value`属性则是该选项的值。在该示例中，第一个选项被设置为占位符，并且其值为空字符串，以便在提交表单时不包含该选项的值。

相关问题

element ui plus select

Element UI Plus的Select组件是基于Element UI的Select组件进行增强和扩展的。它提供了更多的功能和定制选项。

在Element UI Plus的Select组件中，可以通过设置`teleported`属性为`false`，将下拉框插入到父级元素中而不是body元素下。示例代码如下：

<el-select class="search-select" v-model="queryParams.exceptionType" placeholder="选择工作状态" :suffix-icon="IconDropDown" clearable :fit-input-width="true" popper-class="search-select-option" :teleported="false">
  <el-option label="正常" value="0"></el-option>
  <el-option label="异常" value="1"></el-option>
</el-select>

同时，可以通过自定义样式来修改Select组件的外观和弹层位置。示例样式代码如下：

/* el-select 自定义样式（用于选择框） */
.search-select {
  .el-input__wrapper {
    border-radius: 8px;
    height: 44px;
    padding: 0 10px 0 10px;
  }
  .el-input__suffix-inner > :first-child {
    margin: 0;
    width: 32px;
    height: 44px;
  }
  .el-popper {
    top: 46px !important;
  }
}

.search-select-option {
  box-shadow: none !important;
  border-radius: 8px;
  .el-select-dropdown {
    border: 1px solid #147AFC !important;
    box-shadow: none !important;
    border-radius: 8px;
  }
  .el-select-dropdown__item {
    padding: 0;
    margin: 0 16px;
    height: 39px;
    line-height: 39px;
    border-bottom: 1px solid #E8EBF0;
    color: #84878D;
    font-size: 16px;
    font-family: 'AlibabaPuHuiTi-2-55-Regular';
    font-weight: normal;
  }
  .el-select-dropdown__item:last-child {
    border-bottom: none;
  }
  .el-select-dropdown__list {
    margin: 9px 0 !important;
  }
  .el-select-dropdown__item.hover,
  .el-select-dropdown__item:hover {
    background-color: transparent;
  }
  .el-select-dropdown__item.selected {
    color: #147AFC;
  }
}

通过这样的设置和样式修改，可以实现对Element UI Plus的Select组件的定制化需求。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
- *1* *2* [element-plus修改el-select下拉框的位置](https://blog.csdn.net/qq_43651168/article/details/130712253)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 50%"]
- *3* [详解为element-ui的Select和Cascader添加弹层底部操作按钮](https://download.csdn.net/download/weixin_38544781/12928496)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 50%"]
[ .reference_list ]

仿el-select组件

好的，下面是一个仿 Element UI 中 el-select 组件的实现方案。

首先，我们可以创建一个 Select 组件，包含以下几个部分：

1. 输入框：用于显示当前选中的选项或输入搜索关键词。

2. 下拉菜单：用于展示所有可选项。

3. 多选/单选按钮：用于切换多选和单选模式。

4. 清除按钮：用于清除已选中的选项。

下面是 Select 组件的基本代码：

<template>
  <div class="select" :class="{ 'is-multiple': isMultiple, 'is-focus': isFocus }">
    <div class="input-container" @click="toggleMenu">
      <div class="input" :class="{ 'is-placeholder': !selectedOptions.length }">
        <span class="selected-label" v-if="selectedOptions.length">
          <span v-for="(option, index) in selectedOptions" :key="index" class="el-tag el-tag--info">{{ option.label }}</span>
        </span>
        <input type="text" class="input-field" v-model="searchKeyword" :placeholder="placeholder" :readonly="!filterable" @focus="isFocus = true" @blur="isFocus = false">
      </div>
      <i class="el-select__caret el-input__icon el-icon-arrow-up" :class="{ 'el-icon-arrow-down': !isMenuOpen }"></i>
    </div>
    <transition name="el-zoom-in-top">
      <ul class="options" v-show="isMenuOpen">
        <li v-for="(option, index) in filteredOptions" :key="index" @click="selectOption(option)">
          <span class="option-label">{{ option.label }}</span>
          <i class="el-icon-check" v-if="isSelected(option)"></i>
        </li>
        <li v-if="!filteredOptions.length" class="no-data">{{ noDataText }}</li>
      </ul>
    </transition>
    <div class="el-select__tags" v-if="isMultiple">
      <span v-for="(option, index) in selectedOptions" :key="index" class="el-tag el-tag--info">
        {{ option.label }}
        <i class="el-tag__close el-icon-close" @click.stop="removeOption(option)"></i>
      </span>
    </div>
    <div class="el-select__actions" v-if="isMultiple && allowClear">
      <span class="el-select__clear" @click="clearSelection">
        <i class="el-select__clear-icon el-icon-circle-close"></i>
      </span>
    </div>
  </div>
</template>

<script>
export default {
  name: 'Select',
  props: {
    options: {
      type: Array,
      required: true
    },
    value: {
      type: [Object, Array],
      default: null
    },
    placeholder: {
      type: String,
      default: '请选择'
    },
    multiple: {
      type: Boolean,
      default: false
    },
    filterable: {
      type: Boolean,
      default: false
    },
    allowClear: {
      type: Boolean,
      default: false
    },
    noDataText: {
      type: String,
      default: '无匹配数据'
    }
  },
  data () {
    return {
      selectedOptions: [],
      searchKeyword: '',
      isMenuOpen: false,
      isFocus: false
    }
  },
  computed: {
    isMultiple () {
      return this.multiple || Array.isArray(this.value)
    },
    filteredOptions () {
      return this.options.filter(option => option.label.includes(this.searchKeyword))
    },
    selectedValues () {
      return this.selectedOptions.map(option => option.value)
    }
  },
  watch: {
    value (newValue) {
      if (!this.isMultiple) {
        const selectedOption = this.options.find(option => option.value === newValue)
        this.selectedOptions = selectedOption ? [selectedOption] : []
      } else {
        this.selectedOptions = this.options.filter(option => newValue.indexOf(option.value) !== -1)
      }
    },
    selectedOptions (newSelectedOptions) {
      if (!this.isMultiple) {
        const newValue = newSelectedOptions.length ? newSelectedOptions[0].value : null
        this.$emit('input', newValue)
        this.$emit('change', newValue)
      } else {
        const newValue = newSelectedOptions.map(option => option.value)
        this.$emit('input', newValue)
        this.$emit('change', newValue)
      }
    }
  },
  methods: {
    toggleMenu () {
      if (!this.disabled) {
        this.isMenuOpen = !this.isMenuOpen
      }
    },
    selectOption (option) {
      if (!this.isMultiple) {
        this.selectedOptions = [option]
        this.isMenuOpen = false
      } else {
        const index = this.selectedOptions.indexOf(option)
        if (index !== -1) {
          this.selectedOptions.splice(index, 1)
        } else {
          this.selectedOptions.push(option)
        }
      }
    },
    removeOption (option) {
      const index = this.selectedOptions.indexOf(option)
      if (index !== -1) {
        this.selectedOptions.splice(index, 1)
      }
    },
    clearSelection () {
      this.selectedOptions = []
    },
    isSelected (option) {
      return this.selectedValues.indexOf(option.value) !== -1
    }
  }
}
</script>

<style scoped>
.select {
  position: relative;
  display: inline-block;
  width: 200px;
  font-size: 14px;
  color: #606266;
  background-color: #fff;
  border: 1px solid #dcdfe6;
  border-radius: 4px;
  cursor: pointer;
}
.select.is-multiple .input {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  padding: 0 10px;
}
.select.is-multiple .el-select__tags {
  display: flex;
  flex-wrap: wrap;
  padding: 5px 0;
}
.select.is-multiple .el-tag {
  margin-right: 10px;
  margin-bottom: 5px;
  font-size: 12px;
  line-height: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.select.is-multiple .el-tag__close {
  margin-left: 5px;
  cursor: pointer;
}
.select.is-multiple .el-select__actions {
  display: flex;
  align-items: center;
  height: 34px;
  padding-right: 10px;
}
.select.is-multiple .el-select__clear {
  margin-right: 5px;
  font-size: 12px;
  color: #c0c4cc;
  cursor: pointer;
}
.select.is-multiple .el-select__clear:hover {
  color: #909399;
}
.select.is-focus {
  border-color: #409EFF;
  box-shadow: 0 2px 6px rgba(0,0,0,.2);
}
.select.is-focus .el-select__caret {
  color: #409EFF;
}
.select .input-container {
  display: flex;
  align-items: center;
  height: 34px;
  padding: 0 10px;
}
.select .input {
  display: flex;
  align-items: center;
  height: 100%;
  flex: 1;
  overflow: hidden;
}
.select .input.is-placeholder .input-field {
  color: #c0c4cc;
}
.select .input .selected-label {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  margin-right: 5px;
}
.select .input .selected-label .el-tag {
  margin-right: 5px;
  margin-bottom: 5px;
  font-size: 12px;
  line-height: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.select .input .input-field {
  flex: 1;
  border: none;
  outline: none;
  margin-right: 5px;
  font-size: 14px;
  line-height: 1;
  background-color: transparent;
}
.select .el-select__caret {
  color: #dcdfe6;
  font-size: 12px;
  transition: all .3s;
}
.select .el-select__caret.el-icon-arrow-up {
  transform: rotate(-180deg);
}
.select .options {
  position: absolute;
  top: 100%;
  left: 0;
  z-index: 99;
  width: 100%;
  max-height: 250px;
  margin: 0;
  padding: 6px 0;
  background-color: #fff;
  border: 1px solid #dcdfe6;
  border-top: none;
  border-radius: 0 0 4px 4px;
  box-shadow: 0 2px 6px rgba(0,0,0,.2);
  overflow-y: auto;
}
.select .options::-webkit-scrollbar {
  width: 6px;
}
.select .options::-webkit-scrollbar-thumb {
  background-color: rgba(0,0,0,.2);
  border-radius: 3px;
}
.select .options li {
  padding: 6px 12px;
  font-size: 14px;
  color: #606266;
  white-space: nowrap;
  cursor: pointer;
}
.select .options li:hover {
  background-color: #f5f5f5;
}
.select .options li .option-label {
  display: inline-block;
  max-width: 100%;
  overflow: hidden;
  text-overflow: ellipsis;
}
.select .options li .el-icon-check {
  margin-left: 5px;
  color: #409EFF;
}
.select .options li .el-icon-check.disabled {
  color: #c0c4cc;
}
.select .options li.no-data {
  text-align: center;
  color: #c0c4cc;
}
</style>

上面的代码中，props 中的 options 数组包含了所有可选项，每个选项由 label 和 value 两个属性组成。搜索关键词通过 v-model 绑定到 input 输入框中，并且通过 @focus 和 @blur 事件实现了输入框的聚焦和失焦效果。下拉菜单的显示和隐藏通过 v-show 和 isMenuOpen 控制。选中的选项通过 selectedOptions 数组保存，selectOption 方法用于切换选项的选中状态。

如果您需要支持多选功能，可以将 multiple 属性设置为 true。此时，Select 组件会显示一个 el-select__tags 区域，用于展示已选中的选项。同时，也会显示一个 el-select__actions 区域，用于实现清除已选中的选项功能。如果您需要支持清除已选中的选项功能，可以将 allowClear 属性设置为 true。

希望这个仿 Element UI 中 el-select 组件的实现方案可以帮助到您。