I am trying to add the last piece of type in my function, but typescript complained whatever I do. I know there is a way to solve it, and need your help.
export const getPropertiesArray = <T extends object, K extends keyof T>(data: T[], property: K) => {
return data.map(item => item[property]).sort();
};
This is my function and I need to add a default value to property, in this case, the default value is "ID".
Passing default "ID" is not assignable to constraint of object.
Indeed you should assume that ID is always a key of your object.
Here is a workaround:
// T extends { ID: any } - You may replace any by your ID type
export const getPropertiesArray = <T extends { ID: any }>(
data: T[],
property: keyof T = 'ID'
) => {
return data.map(item => item[property]).sort()
}
getPropertiesArray(props.charterers.payload, 'key') calling the function with other key than 'ID' throws an error . Argument of type '"key"' is not assignable to parameter of type '"ID" | undefined'.In general the answer to the question as stated is simple - the format for a default parameter is myParam = "default value", so for example
function myFunc(param1 = "default value") {
//...
}
You can read more about default parameters in Typescript here: https://www.typescriptlang.org/docs/handbook/functions.html#optional-and-default-parameters
HOWEVER: the OP's particular scenario involves a keyof parameter, which requires special handling. See Simon Bruneaud's answer for this.
K declared but its value never used
property = (K) "ID"?