I wrote a simple function to replace values in an array according to a look-up dictionary object:
// typescript
function recode(arr: any[], dict: Record<string, string> ) {
return arr.map(el => dict[el])
}
It works as expected. However, I want the function to return null when array values have no match in the look-up dictionary.
So right now if I do:
// array input
const myArr: string[] = ['eggplant', 'tomato', 'carrot', 'cabbage'];
// look-up dictionary
const myDictionary: Record<string, string> = {
eggplant: 'purple',
tomato: 'red',
carrot: 'orange'
};
function recode(arr: any[], dict: Record<string, string> ) {
return arr.map(el => dict[el])
}
// calling recode()
recode(myArr, myDictionary)
// returns
// ["purple", "red", "orange", undefined]
But I want the output to be
// ["purple", "red", "orange", null]
Is there a simple enough way to achieve this, considering that I'm using typescript (not sure it makes a difference)?
You can use the nullish coalescing operator (??) to resolve null in cases of undefined (and use a generic type parameter to infer the type of values from the dict parameter):
const myArr: string[] = ['eggplant', 'tomato', 'carrot', 'cabbage'];
const myDictionary: Record<string, string> = {
eggplant: 'purple',
tomato: 'red',
carrot: 'orange'
};
function recode <T extends Record<string, any>>(
arr: readonly string[],
dict: T,
): (T[keyof T] | null)[] {
return arr.map(el => dict[el] ?? null);
}
const result = recode(myArr, myDictionary); // (string | null)[]
console.log(result);