A TypeScript function designed to only process arrays consisting of objects that contain a specific property determined by another parameter, with the requirement that this property

Question

A TypeScript function designed to only process arrays consisting of objects that contain a specific property determined by another parameter, with the requirement that this property

function retrieveObjectRow<T = string>(
    arrayData: {
        [key: T]: number;
        [key: string]: unknown;
    }[],
    targetValue: number,
    specifiedField: T
): typeof arrayData[number] | null {
    for (let i = 0; i < arrayData.length; i++) {
        let x = arrayData[i][specifiedField];
        if (Math.abs(x - targetValue) < 0.01) {
            return arrayData[i];
        }
    }
    return null;
}

The function is designed to work with arrays of objects as the first parameter, where the objects must have a property specified in the third parameter, and this property must be numeric. Please provide the correct typing.

Here are some examples of how to use this function:

const DATA_OBJECTS = [
  { a: 1, b: 'first' },
  { a: 2, b: 'second' },
];
retrieveObjectRow(DATA_OBJECTS, 2.005, 'a'); // OK, returns the second row
retrieveObjectRow(DATA_OBJECTS, 5, 'a'); // OK, returns null
retrieveObjectRow(DATA_OBJECTS, 1.005, 'b'); // Not OK, should trigger a TS error because the property 'b' is not numeric

In summary, the array provided in the first parameter may contain objects with any properties, but it is mandatory to have a numeric property specified as a string in the third parameter.

typescript

Answer 1

Answer №1

If you're looking to streamline your function signature, one suggestion is to utilize a helper type that can extract keys mapping to values of type number. Here's an example of how you can define such a type:

type NumberKeys<T> = {
    [K in keyof T]: T[K] extends number ? K : never;
}[keyof T];

By incorporating this utility type, you can simplify the function definition by specifying the field as a parameter, rather than trying to enforce the restriction within the generic type. Here's how you can update your function:

function findRecord<T extends Record<string, any>>(data: T[], value: number, key: NumberKeys<T>): T { /* ... */ }

With this revised signature, you should see the desired inferences in action:

const DATA = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
];

findRecord(DATA, 2.5, 'id'); // Returns record with id 2
findRecord(DATA, 5, 'id'); // Returns null
findRecord(DATA, 1.5, 'name'); // Argument of type '"name"' is not assignable to parameter of type '"id"'.

Answer 2

If you're looking to streamline your function signature, one suggestion is to utilize a helper type that can extract keys mapping to values of type number. Here's an example of how you can define such a type:

type NumberKeys<T> = {
    [K in keyof T]: T[K] extends number ? K : never;
}[keyof T];

By incorporating this utility type, you can simplify the function definition by specifying the field as a parameter, rather than trying to enforce the restriction within the generic type. Here's how you can update your function:

function findRecord<T extends Record<string, any>>(data: T[], value: number, key: NumberKeys<T>): T { /* ... */ }

With this revised signature, you should see the desired inferences in action:

const DATA = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
];

findRecord(DATA, 2.5, 'id'); // Returns record with id 2
findRecord(DATA, 5, 'id'); // Returns null
findRecord(DATA, 1.5, 'name'); // Argument of type '"name"' is not assignable to parameter of type '"id"'.

A TypeScript function designed to only process arrays consisting of objects that contain a specific property determined by another parameter, with the requirement that this property

Answer №1

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