Use of instanceof in TypeScript
Consider this basic node+ts code:
import * as express from "express";
function doStuff(app: express.Application) {
if (!(app instanceof express.Application)) throw new TypeError();
// etc...
}
VSCode shows me this error for ...instanceof express.Application...:
[ts] Property 'Application' does not exist on type 'typeof e'. [2339]
What am I doing wrong?
node.js typescript express
asked Jan 20 at 6:52
lonixlonix
458110
add a comment |
Consider this basic node+ts code:
import * as express from "express";
function doStuff(app: express.Application) {
if (!(app instanceof express.Application)) throw new TypeError();
// etc...
}
VSCode shows me this error for ...instanceof express.Application...:
[ts] Property 'Application' does not exist on type 'typeof e'. [2339]
What am I doing wrong?
node.js typescript express
asked Jan 20 at 6:52
lonixlonix
458110
add a comment |
Consider this basic node+ts code:
import * as express from "express";
function doStuff(app: express.Application) {
if (!(app instanceof express.Application)) throw new TypeError();
// etc...
}
VSCode shows me this error for ...instanceof express.Application...:
[ts] Property 'Application' does not exist on type 'typeof e'. [2339]
What am I doing wrong?
node.js typescript express
asked Jan 20 at 6:52
lonixlonix
458110
Consider this basic node+ts code:
import * as express from "express";
function doStuff(app: express.Application) {
if (!(app instanceof express.Application)) throw new TypeError();
// etc...
}
VSCode shows me this error for ...instanceof express.Application...:
[ts] Property 'Application' does not exist on type 'typeof e'. [2339]
What am I doing wrong?
node.js typescript express
node.js typescript express
asked Jan 20 at 6:52
lonixlonix
458110
asked Jan 20 at 6:52
lonixlonix
458110
asked Jan 20 at 6:52
lonixlonix
458110
asked Jan 20 at 6:52
lonixlonix
458110
asked Jan 20 at 6:52
lonixlonix
458110
458110
add a comment |
add a comment |
1 Answer
1
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oldest
votes
instanceof is a Javascript operator. The right hand side operand must be a runtime value (a function or a constructor) for it to work.
express.Application is defined as an interface. Interfaces only exist at compile time to aid in type checking. This means at runtime, there is no express.Application value to be the operand in the instanceof operation, and so typescript issues an error.
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
1
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
add a comment |
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1 Answer
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active
oldest
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
instanceof is a Javascript operator. The right hand side operand must be a runtime value (a function or a constructor) for it to work.
express.Application is defined as an interface. Interfaces only exist at compile time to aid in type checking. This means at runtime, there is no express.Application value to be the operand in the instanceof operation, and so typescript issues an error.
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
1
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
add a comment |
instanceof is a Javascript operator. The right hand side operand must be a runtime value (a function or a constructor) for it to work.
express.Application is defined as an interface. Interfaces only exist at compile time to aid in type checking. This means at runtime, there is no express.Application value to be the operand in the instanceof operation, and so typescript issues an error.
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
1
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
add a comment |
instanceof is a Javascript operator. The right hand side operand must be a runtime value (a function or a constructor) for it to work.
express.Application is defined as an interface. Interfaces only exist at compile time to aid in type checking. This means at runtime, there is no express.Application value to be the operand in the instanceof operation, and so typescript issues an error.
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
instanceof is a Javascript operator. The right hand side operand must be a runtime value (a function or a constructor) for it to work.
express.Application is defined as an interface. Interfaces only exist at compile time to aid in type checking. This means at runtime, there is no express.Application value to be the operand in the instanceof operation, and so typescript issues an error.
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
answered Jan 20 at 7:51
Titian Cernicova-DragomirTitian Cernicova-Dragomir
64k34159
64k34159
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
1
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
add a comment |
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
1
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
Thanks that makes sense. I could use duck typing to achieve the same result, though that's messy... is there an alternative?
– lonix
Jan 20 at 8:10
1
1
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
@Ionix As the type is defined you can only check if specific properties exist
– Titian Cernicova-Dragomir
Jan 20 at 8:15
add a comment |
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