Error Duplicate Const Declaration in Switch Case Statement

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?

Answers:

Answer

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

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

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

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
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.

Answer

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 wont use return you must declare a let query_url above your switch statement.

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