microsoft / microsoft/TypeScript
The union type gives a warning when +=
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Description
Bug Report
The union type gives a warning when + =
🔎 Search Terms
+= |
🕗 Version & Regression Information
- This is a crash
- This changed between versions 4.1.3 and 4.2.3
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
- I was unable to test this on prior versions because _______
⏯ Playground Link
Playground link with relevant code
💻 Code
let a: number | string = 0
// error
a += 'px'
// normal
a = a + 'px'
🙁 Actual behavior
🙂 Expected behavior
noError
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the linked TypeScript Playground and compare the union-typed variable's += expression with the equivalent assignment expression shown in the report. Trace the type-checking behavior for compound assignment and confirm the work is done when the reported warning is no longer produced while the existing assignment behavior remains unchanged.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 45/100