Duplicate variable names in switch/case [duplicate] - ecmascript-6

Question

I have the following code and I get the error 'Duplicate Declaration 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?

Answer 1

Try wrapping the cases in blocks:
switch(condition) {
case 'complex': {
const query_url = `something`;
… // do something
break;
}
default: {
const query_url = `something`;
… // do something else
break;
}
}

Answer 2

I personally prefer (and tend to abuse) the following in these sorts of cases:
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)
Update: Alternatively, much more compact depending on if there is any logic there or if it's a simple assignment:
const query_url = {complex : 'something'}[condition] || 'something-else';
Also, of course, depends on the amount of outside-logic embedded in those switch statements!

Answer 3

if you need to redeclare the same variable in each case see #Bergi 's answer bellow
if query_url can have multiple values depending on the switch branch obviously you need a variable ( declare either with var or let ).
const is set once and stays that way.
example usage with let
let query_url = '';
switch(condition) {
case 'complex':
query_url = `something`;
break;
default:
query_url = `something`;
break;
}

Answer 4

You can use {} to scope your switch case.
For your case, you need to return the variable as long as the var exists and is accessible between curly braces:
switch(condition) {
case 'complex': {
const query_url = `something`;
return query_url;
}
default: {
const query_url = `something`;
return query_url;
}
}
If you won't use return, you must declare a let query_url above your switch statement.

Answer 5

Just put your switch in a function with some return statements :
var condition;
function aSwitch(condition){
switch(condition) {
case 'complex':
return 'something';
default:
return 'something';
}
}
const query_url = aSwitch(condition);

Answer 6

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.