Javascript Switch Case 语句中的重复常量声明错误
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Error Duplicate Const Declaration in Switch Case Statement
提问by asanas
I have the following code and I get the error 'Duplicate Declaration query_url'.
我有以下代码，但收到错误“重复声明 query_url”。
switch(condition) {
case 'complex':
const query_url = `something`;
break;
default:
const query_url = `something`;
break;
}
I understand that query_url is getting declared twice which isn't right. But i don't know how to resolve this. Can someone please help on what should be the correct way to make this work?
我知道 query_url 被声明了两次，这是不对的。但我不知道如何解决这个问题。有人可以帮助了解进行这项工作的正确方法吗？
采纳答案by eltonkamami
if query_urlcan have multiple values depending on the switch branch obviously you need a variable ( declare either with varor let).
ifquery_url可以根据 switch 分支有多个值，显然你需要一个变量（声明 withvar或let）。
const is set once and stays that way.
const 设置一次并保持这种状态。
example usage with let
let 的示例用法
let query_url = '';
switch(condition) {
case 'complex':
query_url = `something`;
break;
default:
query_url = `something`;
break;
}
回答by Bergi
Try wrapping the cases in blocks:
尝试将案例包装在块中：
switch(condition) {
case 'complex': {
const query_url = `something`;
… // do something
break;
}
default: {
const query_url = `something`;
… // do something else
break;
}
}
回答by rob2d
I personally prefer (and tend to abuse) the following in these sorts of cases:
在这些情况下，我个人更喜欢（并倾向于滥用）以下内容：
const query_url = (()=>
{
switch(condition)
case 'complex': return 'something';
default : return 'something-else';
})();
(this requires ES6 or declaring "use-strict" in Node 4.x though)
（这需要 ES6 或在 Node 4.x 中声明“use-strict”）
Update: Alternatively, much more compact depending on if there is any logic there or if it's a simple assignment:
更新：或者，更紧凑，具体取决于那里是否有任何逻辑或者它是否是一个简单的分配：
const query_url = {complex : 'something'}[condition] || 'something-else';
Also, of course, depends on the amount of outside-logic embedded in those switch statements!
当然，也取决于嵌入在这些 switch 语句中的外部逻辑的数量！
回答by Zakaria
Just put your switchin a function with some return statements :
只需将您switch的函数放入带有一些返回语句的函数中：
var condition;
function aSwitch(condition){
switch(condition) {
case 'complex':
return 'something';
default:
return 'something';
}
}
const query_url = aSwitch(condition);
回答by sbk201
const query_url={
complex:'something complex',
other:'other thing'
}[condition]
The drawback is,you can't have default with object,you need to have addition check of condition.
缺点是，你不能有对象的默认值，你需要额外检查条件。
