Javascript真条件未检测到布尔值

Question

I have this part of code:

   let values = true;

let msg = 'message1';
        if(values) {let msg = 'message2';}

        console.log(msg);

And I always have message1 in console log.

As I know, the if(values) should satisfy the if statement for any truthy value of values including true, any non-zero number, any non-empty string value, any object or array reference, etc...

So why is it not working?

Answer 1

There are no issues with if statement. It's correctly running but the problem is that you have defined msg variable again with let msg = 'message2';

That should be replaced with msg = 'message2' and it will work.

 let values = true; let msg = 'message1'; if(values) { msg = 'message2'; } console.log(msg);

Answer 2

The scope of a variable declared using let is the most inner block of code that contains it.

In your example there are two different variables named msg .

The first one ( let msg = 'message1') is the one printed by console.log(msg);`.

The second one (let msg = 'message2') exists only in the block ( {...} ) where it is declared. It is destroyed when the code execution leaves the block (at } ).
Inside that block the outer variable named msg is not available.

There is no need to declare a variable multiple times (unless your purpose is to get the effect you encountered now). Declare it only once, before it is used for the first time.

This code works as expected:

let values = true;
let msg = 'message1';

if (values) {
  msg = 'message2';
}

console.log(msg);

You can add a console.log() calls inside the if block to check that it is executed (because the condition is true ):

 let values = true; let msg = 'message1'; if (values) { let msg = 'message2'; console.log('inner: ' + msg); } console.log('outer: ' + msg);