typescript how to use type guard for key-value
1
type Dircory<T> {
[key:string]: T
}
function colname(columns:Array<string> | string| Dictory<string>, name){
if(Array.isArray(columns){
return columns.map(column=>table_name + "." + columns);
}else if(typeof columns == "string"){
return table_name + "." + columns;
}else if(typeof columns == "object"){
return columns as Dictory<string>
}
}
That's my code, but the return type of colname always Dictory<string> whatever pass any type, how should I correctly use type guard for key-value
typescript
asked Nov 19 '18 at 10:02
s97712s97712
256
add a comment |
1
type Dircory<T> {
[key:string]: T
}
function colname(columns:Array<string> | string| Dictory<string>, name){
if(Array.isArray(columns){
return columns.map(column=>table_name + "." + columns);
}else if(typeof columns == "string"){
return table_name + "." + columns;
}else if(typeof columns == "object"){
return columns as Dictory<string>
}
}
That's my code, but the return type of colname always Dictory<string> whatever pass any type, how should I correctly use type guard for key-value
typescript
asked Nov 19 '18 at 10:02
s97712s97712
256
Could you provide the specific values you are passing and where the actual result differs from your expected result?
– Sefe
Nov 19 '18 at 10:09
add a comment |
1
1
1
type Dircory<T> {
[key:string]: T
}
function colname(columns:Array<string> | string| Dictory<string>, name){
if(Array.isArray(columns){
return columns.map(column=>table_name + "." + columns);
}else if(typeof columns == "string"){
return table_name + "." + columns;
}else if(typeof columns == "object"){
return columns as Dictory<string>
}
}
That's my code, but the return type of colname always Dictory<string> whatever pass any type, how should I correctly use type guard for key-value
typescript
asked Nov 19 '18 at 10:02
s97712s97712
256
type Dircory<T> {
[key:string]: T
}
function colname(columns:Array<string> | string| Dictory<string>, name){
if(Array.isArray(columns){
return columns.map(column=>table_name + "." + columns);
}else if(typeof columns == "string"){
return table_name + "." + columns;
}else if(typeof columns == "object"){
return columns as Dictory<string>
}
}
That's my code, but the return type of colname always Dictory<string> whatever pass any type, how should I correctly use type guard for key-value
typescript
typescript
asked Nov 19 '18 at 10:02
s97712s97712
256
asked Nov 19 '18 at 10:02
s97712s97712
256
asked Nov 19 '18 at 10:02
s97712s97712
256
asked Nov 19 '18 at 10:02
s97712s97712
256
asked Nov 19 '18 at 10:02
s97712s97712
256
256
Could you provide the specific values you are passing and where the actual result differs from your expected result?
– Sefe
Nov 19 '18 at 10:09
add a comment |
Could you provide the specific values you are passing and where the actual result differs from your expected result?
– Sefe
Nov 19 '18 at 10:09
Could you provide the specific values you are passing and where the actual result differs from your expected result?
– Sefe
Nov 19 '18 at 10:09
Could you provide the specific values you are passing and where the actual result differs from your expected result?
– Sefe
Nov 19 '18 at 10:09
add a comment |
1 Answer
1
active
oldest
votes
1
The problem is not with the type guard. If you want the function to return a value of the same type you will either need to have multiple overloads, or a type parameter that captures the actual type of the parameter and return the same type parameter:
type Dircory<T> = {
[key: string]: T
}
let table_name;
function colname<T extends Array<string> | string | Dircory<string>>(columns: T, name: string) :T
function colname(columns: Array<string> | string | Dircory<string>, name) {
if (Array.isArray(columns)) {
return columns.map(column => table_name + "." + columns);
} else if (typeof columns == "string") {
return table_name + "." + columns;
} else if (typeof columns == "object") {
return columns as Dircory<string>
}
}
let a = colname("A", ""); // string, actually the string literal type "A", but will work with strnig vars too
let arr = colname(["A"], ""); // string
let d = colname({a: "A"}, ""); // { a: string; }
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
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oldest
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oldest
votes
1
The problem is not with the type guard. If you want the function to return a value of the same type you will either need to have multiple overloads, or a type parameter that captures the actual type of the parameter and return the same type parameter:
type Dircory<T> = {
[key: string]: T
}
let table_name;
function colname<T extends Array<string> | string | Dircory<string>>(columns: T, name: string) :T
function colname(columns: Array<string> | string | Dircory<string>, name) {
if (Array.isArray(columns)) {
return columns.map(column => table_name + "." + columns);
} else if (typeof columns == "string") {
return table_name + "." + columns;
} else if (typeof columns == "object") {
return columns as Dircory<string>
}
}
let a = colname("A", ""); // string, actually the string literal type "A", but will work with strnig vars too
let arr = colname(["A"], ""); // string
let d = colname({a: "A"}, ""); // { a: string; }
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
add a comment |
1
The problem is not with the type guard. If you want the function to return a value of the same type you will either need to have multiple overloads, or a type parameter that captures the actual type of the parameter and return the same type parameter:
type Dircory<T> = {
[key: string]: T
}
let table_name;
function colname<T extends Array<string> | string | Dircory<string>>(columns: T, name: string) :T
function colname(columns: Array<string> | string | Dircory<string>, name) {
if (Array.isArray(columns)) {
return columns.map(column => table_name + "." + columns);
} else if (typeof columns == "string") {
return table_name + "." + columns;
} else if (typeof columns == "object") {
return columns as Dircory<string>
}
}
let a = colname("A", ""); // string, actually the string literal type "A", but will work with strnig vars too
let arr = colname(["A"], ""); // string
let d = colname({a: "A"}, ""); // { a: string; }
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
add a comment |
1
1
1
The problem is not with the type guard. If you want the function to return a value of the same type you will either need to have multiple overloads, or a type parameter that captures the actual type of the parameter and return the same type parameter:
type Dircory<T> = {
[key: string]: T
}
let table_name;
function colname<T extends Array<string> | string | Dircory<string>>(columns: T, name: string) :T
function colname(columns: Array<string> | string | Dircory<string>, name) {
if (Array.isArray(columns)) {
return columns.map(column => table_name + "." + columns);
} else if (typeof columns == "string") {
return table_name + "." + columns;
} else if (typeof columns == "object") {
return columns as Dircory<string>
}
}
let a = colname("A", ""); // string, actually the string literal type "A", but will work with strnig vars too
let arr = colname(["A"], ""); // string
let d = colname({a: "A"}, ""); // { a: string; }
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
The problem is not with the type guard. If you want the function to return a value of the same type you will either need to have multiple overloads, or a type parameter that captures the actual type of the parameter and return the same type parameter:
type Dircory<T> = {
[key: string]: T
}
let table_name;
function colname<T extends Array<string> | string | Dircory<string>>(columns: T, name: string) :T
function colname(columns: Array<string> | string | Dircory<string>, name) {
if (Array.isArray(columns)) {
return columns.map(column => table_name + "." + columns);
} else if (typeof columns == "string") {
return table_name + "." + columns;
} else if (typeof columns == "object") {
return columns as Dircory<string>
}
}
let a = colname("A", ""); // string, actually the string literal type "A", but will work with strnig vars too
let arr = colname(["A"], ""); // string
let d = colname({a: "A"}, ""); // { a: string; }
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
answered Nov 19 '18 at 10:11
Titian Cernicova-DragomirTitian Cernicova-Dragomir
65.1k34361
65.1k34361
add a comment |
add a comment |
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Could you provide the specific values you are passing and where the actual result differs from your expected result?
– Sefe
Nov 19 '18 at 10:09