表达“东西”？ “ Something”：“别的东西”更短？

Question

快速提问。我可以用更短的方式写吗？

{this.state.members[activeMemberId].id ? this.state.members[activeMemberId].id : null}

例如

{this.state.members[activeMemberId].id ? <-the same : null}

Answer 1

您可以这样做：

if ((byte & 0xE7) == 0x26) {
    /* This `byte` is a ES, SS, CS or DS segment override prefix */
}
if ((byte & 0xFC) == 0x64) {
    /* This `byte` is a FS, GS, Operand-size or address-size override prefix */
}
if ((byte & 0xFC) == 0xF0) {
    if (byte != 0xF1) {
        /* This `byte` is a LOCK, REPN(E/Z) or REP(_/E/Z) prefix */
    }
}

Answer 2

您可以使用逻辑OR

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.6.10/vue.min.js"></script>
<script src="https://unpkg.com/vue-select@latest"></script>
<link rel="stylesheet" href="https://unpkg.com/vue-select@latest/dist/vue-select.css">

<div id="app">
  <div>
    <v-select v-model="selected" :options="options">
      <template v-slot:option="option">
        {{ option.id }} - {{ option.name }}  
      </template>
      <template v-slot:selected-option="option">
        {{ option.id }} - {{ option.name }}
      </template>
    </v-select>
    <div v-if="selected !== ''" style="margin-top: 20px;">
      <hr/> Selected Item:
      <pre>{{ selected }}</pre>
      <hr/>
    </div>
    <div v-if="selected !== ''" style="margin-top:20px;">
      Name:
      <div>
        <input type="text" v-model="selected.name" />
      </div>
      ID:
      <div>
        <input type="text" v-model="selected.id" />
      </div>
      <hr/>
    </div>
  </div>
</div>

这是如何工作的？

{ this.state.members[activeMemberId].id || null }

拇指规则：- 逻辑或返回第一个真值，如果还有其他则返回最后一个值

Answer 3

您可以使用||

this.state.members[activeMemberId].id || null

Answer 4

请小心不要试图访问undefined的id属性时得到未定义的引用异常

function getMemberId(activeMemberId) {
    this.state = { members: {
      id1: { id: 1 }
    } };
    const { members: { [activeMemberId]: { id = null } = {} } = {} } = this.state;
    return id;
 }
 
 console.log(getMemberId('id1'));
 console.log(getMemberId('id2'));
 
 // Or you could chain the && operator and || operator
 function getMemberIdAlt(activeMemberId) {
    this.state = { members: {
      id1: { id: 1 }
    } };
    
    return (
      this.state
      && this.state.members
      && this.state.members[activeMemberId]
      && this.state.members[activeMemberId].id
    ) || null;
 }
 
 console.log(getMemberIdAlt('id1'));
 console.log(getMemberIdAlt('id2'));