Typescript cannot find interface name but know the function defined

Question

Why here ReadStream and WriteStream cannot been identified by typescript, while function fs.createReadStream() can be identified? If compile, errors below throw:

app1.ts(3,8): error TS2304: Cannot find name 'ReadStream'.
app1.ts(4,8): error TS2304: Cannot find name 'WriteStream'.

All the interfaces and functions are defined in node.d.ts file.

Just an FYI, it's generally preferred for questions to have their code included as text rather than as an image. — Joe Clay
– Joe Clay, Commented Jan 6, 2017 at 15:30
:) I just want people to see the red wave lines. The code here is not so important. Thanks for your reminder anyway. — BartMao
– BartMao, Commented Jan 6, 2017 at 15:37
Curious as to why you are doing this. In my experience simply assigning the output of createReadStream will assign the stream to rs. Why the interface invocation? — Paul Stoner
– Paul Stoner, Commented Jan 6, 2017 at 15:40
Doing this so that can clearly see the type of the variable sometimes, and if a variable like ws is declared but not assigned yet, its type must be explicitly declared, right? The syntax is right anyway, isn't? Maybe I have been affected by some other strong typed languages:) — BartMao
– BartMao, Commented Jan 6, 2017 at 15:51

Ayman Nedjmeddine · Accepted Answer · 2017-01-09 17:53:07Z

2

You're variable declaration should be like:

let rs: fs.ReadStream = ...

This way you're telling TypeScript 'hey, these vars are ReadStreams which you can find the declaration in the fs module'.

answered Jan 9, 2017 at 17:53

Ayman Nedjmeddine

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BartMao · Accepted Answer · 2017-01-07 06:47:19Z

0

After digging into the definition file, I realized I should append the module name before the interface ReadStream or WriteStream:

import fs = require('fs');
let ws:fs.WriteStream

answered Jan 7, 2017 at 6:47

BartMao

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