Why isn't "a.length > 0" an type-guard that help me Narrowing?

[aiden271828]

Bug Report

🔎 Search Terms

array length narrowing

🕗 Version & Regression Information

• This is a crash
• This changed versions is 4.4.4

⏯ Playground Link

Playground link with relevant code

💻 Code

const a:object[] = []
/**
* It can be 'push' 0 or multiple times.
* a[] is an array of arbitrary length
*/
a.push({});a.push({});a.push({});a.push({});a.push({});
while (a.length > 0) {
  // obj: object | undefined
  const obj = a.pop()
  // Object is possibly 'undefined'.
  console.log(obj.toString)
}

🙁 Actual behavior

Object is possibly 'undefined'.

I've obviously determined that the a [] length is greater than zero, which means pop cannot return undefined.

But TS is still telling me that obj might be undefined.I had to useconst obj = a.pop()! to make right.

Is this a bug or is ts not implemented？

If not implemented, Why didn't you do it(I'm very interested in it) ?

🙂 Expected behavior

obj type is not included undefined

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[MartinJohns]

Duplicate of #30406. Used search terms: array pop in:title