错误 TS2532：对象可能是“未定义” - 使用“？” 操作员

Question

I use TS 4.0.2, and get an error while using "?." operator:

When I use the old nullish check, it run:

if (a && a.length) { 

What do I miss?

Answer 1

If you read the documentation | 3.7 you will see that.

That might result in dividing undefined, which is why in strictNullChecks, the following is an error.

function barPercentage(foo?: { bar: number }) {
  return foo?.bar / 100;
  //     ~~~~~~~~
  // Error: Object is possibly undefined.
}

I believe that this is the case.