Typescript: Multiple brackets field declaration
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I found this expression in a project:
export class MyComponent implements OnInit {
public field: { [key: number] : string } = something
...
}
and I don't know what it means. Can anyone explain this and give me a reference, so I can learn this type of declarations?
typescript
asked Nov 16 '18 at 13:08
MTZMTZ
96114
add a comment |
I found this expression in a project:
export class MyComponent implements OnInit {
public field: { [key: number] : string } = something
...
}
and I don't know what it means. Can anyone explain this and give me a reference, so I can learn this type of declarations?
typescript
asked Nov 16 '18 at 13:08
MTZMTZ
96114
add a comment |
I found this expression in a project:
export class MyComponent implements OnInit {
public field: { [key: number] : string } = something
...
}
and I don't know what it means. Can anyone explain this and give me a reference, so I can learn this type of declarations?
typescript
asked Nov 16 '18 at 13:08
MTZMTZ
96114
I found this expression in a project:
export class MyComponent implements OnInit {
public field: { [key: number] : string } = something
...
}
and I don't know what it means. Can anyone explain this and give me a reference, so I can learn this type of declarations?
typescript
typescript
asked Nov 16 '18 at 13:08
MTZMTZ
96114
asked Nov 16 '18 at 13:08
MTZMTZ
96114
asked Nov 16 '18 at 13:08
MTZMTZ
96114
asked Nov 16 '18 at 13:08
MTZMTZ
96114
asked Nov 16 '18 at 13:08
MTZMTZ
96114
96114
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
field is an object type (because of the {}) that has a numeric index signature that returns a string. This means that an object assigned to the field can only have numeric keys and the values in the object must be of type string
let field: { [key: number]: string };
field = {
0: "A",
//"A": "A", // error key is not numeric
//0: 0, // error value is not a string
}
let a = field[0] //a is string
field = ["A", "B"] // arrays are valid as well
You can read more about it here
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
Do you meanais a string, right?
– MTZ
Nov 16 '18 at 13:46
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,keyandnameare common choices, but any name will do
– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
add a comment |
{ [key: number] : string }
is an anonymous/inline type declaration, it translates to:
interface Anon {
[key: number]: string;
}
The brackets are declare, that the type of any undeclared additional property in that object has to be of type number and the value of that type must be a string.
{ 1: "foo", 2: "bar" } // valid
{ "1": "foo", "2": "bar" } // invalid
http://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types-and-string-index-signatures
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
field is an object type (because of the {}) that has a numeric index signature that returns a string. This means that an object assigned to the field can only have numeric keys and the values in the object must be of type string
let field: { [key: number]: string };
field = {
0: "A",
//"A": "A", // error key is not numeric
//0: 0, // error value is not a string
}
let a = field[0] //a is string
field = ["A", "B"] // arrays are valid as well
You can read more about it here
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
Do you meanais a string, right?
– MTZ
Nov 16 '18 at 13:46
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,keyandnameare common choices, but any name will do
– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
add a comment |
field is an object type (because of the {}) that has a numeric index signature that returns a string. This means that an object assigned to the field can only have numeric keys and the values in the object must be of type string
let field: { [key: number]: string };
field = {
0: "A",
//"A": "A", // error key is not numeric
//0: 0, // error value is not a string
}
let a = field[0] //a is string
field = ["A", "B"] // arrays are valid as well
You can read more about it here
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
Do you meanais a string, right?
– MTZ
Nov 16 '18 at 13:46
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,keyandnameare common choices, but any name will do
– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
add a comment |
field is an object type (because of the {}) that has a numeric index signature that returns a string. This means that an object assigned to the field can only have numeric keys and the values in the object must be of type string
let field: { [key: number]: string };
field = {
0: "A",
//"A": "A", // error key is not numeric
//0: 0, // error value is not a string
}
let a = field[0] //a is string
field = ["A", "B"] // arrays are valid as well
You can read more about it here
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
field is an object type (because of the {}) that has a numeric index signature that returns a string. This means that an object assigned to the field can only have numeric keys and the values in the object must be of type string
let field: { [key: number]: string };
field = {
0: "A",
//"A": "A", // error key is not numeric
//0: 0, // error value is not a string
}
let a = field[0] //a is string
field = ["A", "B"] // arrays are valid as well
You can read more about it here
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
edited Nov 16 '18 at 13:50
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
answered Nov 16 '18 at 13:14
Titian Cernicova-DragomirTitian Cernicova-Dragomir
73k35270
73k35270
Do you meanais a string, right?
– MTZ
Nov 16 '18 at 13:46
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,keyandnameare common choices, but any name will do
– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
add a comment |
Do you meanais a string, right?
– MTZ
Nov 16 '18 at 13:46
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,keyandnameare common choices, but any name will do
– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
Do you mean
a is a string, right?– MTZ
Nov 16 '18 at 13:46
Do you mean
a is a string, right?– MTZ
Nov 16 '18 at 13:46
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin yes, my bad, fixed :)
– Titian Cernicova-Dragomir
Nov 16 '18 at 13:50
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,
key and name are common choices, but any name will do– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
@MateutAlin no, it's just the name of the index parameter , it can be any name you want,
key and name are common choices, but any name will do– Titian Cernicova-Dragomir
Nov 16 '18 at 14:03
add a comment |
{ [key: number] : string }
is an anonymous/inline type declaration, it translates to:
interface Anon {
[key: number]: string;
}
The brackets are declare, that the type of any undeclared additional property in that object has to be of type number and the value of that type must be a string.
{ 1: "foo", 2: "bar" } // valid
{ "1": "foo", "2": "bar" } // invalid
http://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types-and-string-index-signatures
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
add a comment |
{ [key: number] : string }
is an anonymous/inline type declaration, it translates to:
interface Anon {
[key: number]: string;
}
The brackets are declare, that the type of any undeclared additional property in that object has to be of type number and the value of that type must be a string.
{ 1: "foo", 2: "bar" } // valid
{ "1": "foo", "2": "bar" } // invalid
http://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types-and-string-index-signatures
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
add a comment |
{ [key: number] : string }
is an anonymous/inline type declaration, it translates to:
interface Anon {
[key: number]: string;
}
The brackets are declare, that the type of any undeclared additional property in that object has to be of type number and the value of that type must be a string.
{ 1: "foo", 2: "bar" } // valid
{ "1": "foo", "2": "bar" } // invalid
http://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types-and-string-index-signatures
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
{ [key: number] : string }
is an anonymous/inline type declaration, it translates to:
interface Anon {
[key: number]: string;
}
The brackets are declare, that the type of any undeclared additional property in that object has to be of type number and the value of that type must be a string.
{ 1: "foo", 2: "bar" } // valid
{ "1": "foo", "2": "bar" } // invalid
http://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types-and-string-index-signatures
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
answered Nov 16 '18 at 13:14
Josef FazekasJosef Fazekas
30037
30037
add a comment |
add a comment |
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