--format=iife option erases variables defined multiple times

[melpon]

test.js:

var x = 10;
console.log(x);
var x = 20;

Output from the esbuild --format=iife test.js command:

(() => {
  console.log(x);
  var x = 20;
})();

The former program outputs 10, while the latter outputs undefined. Is this behavior intended?

[melpon]

I found #2080. It seems to same problem.