microsoft / microsoft/TypeScript
`deleteCount` param to `splice()` is not optional in es5 types
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Description
TypeScript Version: 3.5.1
Search Terms: splice deleteCount
Code
Set the target to ES5 then
[1, 2, 3].splice(0); // should error. deleteCount missing
[1, 2, 3].splice(0, 3); // ok
Expected behavior:
[1, 2, 3].splice(0); not allowed
Actual behavior:
[1, 2, 3].splice(0); allowed
Playground Link: this
deleteCount only become optional in ES6
ES5: https://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.12
ES6: https://www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.splice
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 by reproducing the example in the TypeScript Playground with the target set to ES5, then compare the ES5 and ES6 declarations for Array.splice. The fix is complete when ES5 rejects an omitted deleteCount while ES6 continues to allow it.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 45/100