Here's a map I have:
const Map = {
key1: 'value1',
key2: 'value2'
}
I'm looking to create a type value1 | value2 using the object above. Is there a way to do this without repeating the values?
I attempted
type MyType = Map.key1 | Map.key2Cannot find namespace 'Map'
To start, it's important to define the MyMap variable with the as const keyword.
const MyMap = {
key1: 'value1',
key2: 'value2'
} as const
By doing this, TypeScript understands that the string literals within the object are specific constants and not just general strings.
You can then determine the type of that object using the typeof operator, and access all possible values by indexing that type with its own keys:
type MyMapValues = typeof MyMap[keyof typeof MyMap] // "value1" | "value2"
const a: MyMapValues = "value1"
const b: MyMapValues = "value2"
// Error: Only allowed values can be assigned:
const c: MyMapValues = "value3"
let NewArray = [
{ name: "Alice", age: 15 },
{ name: "Bob", age: 23 },
{ name: "Eve", age: 38 }
];
type X = (typeof NewArray)[number];
const info = {
value: 123,
text: 'text',
subInfo: {
value: false
}
};
type InfoData = typeof info;
Accessing the map index will retrieve the value, but not the specific data type. By utilizing this method, you can ascertain the data type of the values.
const myMap = {
key1: 'value1',
key2: 'value2'
}
type myType = typeof myMap["key1"] | typeof myMap["key1"]
If you want your keys to have a specific type, they should be declared as constants using the keyword const.
You can define the type like this:
const Data = {
key1: 'value1',
key2: 'value2'
} as const;
type DataType = typeof Data[keyof typeof Data];
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