Dynamic Typescript Object Properties from Function Arguments

Question

I have a function that takes in a n number of arguments, and generates a new object containing a key-value map of the arguments to a unique hash.

Is there a way for Typescript to dynamically infer the keys of the returned object from the arguments of the function?

Example,

CreateActionType function that generates the dictionary:

function createActionType<K extends {} | void>(...type: string[]): Readonly<{ [key: string]: string }> {
    const actions = {};

    type.forEach((item: string) => {
        actions[item] = `${item}/${generateUniqueId()}`;
    });

    return Object.freeze(actions);
};

Using createActionType:

interface ActionTypes {
    MY_ACTION_1, 
    MY_ACTION_2
}

const action = createActionType<ActionTypes>("MY_ACTION_1", "MY_ACTION_2");
/*
 * action contains { MY_ACTION_1: "MY_ACTION_1/0", MY_ACTION_2: "MY_ACTION_2/1" }
 */
action.MY_ACTION_1; // returns "MY_ACTION_1/0"

I would like to remove the duplication, and just call createActionType like:

const action = createActionType("MY_ACTION_1", "MY_ACTION_2");
action.MY_ACTION_1;  // Intellisense will be able to infer the properties 
                     // MY_ACTION_1 and MY_ACTION_2 from action

dpaulus · Accepted Answer · 2017-04-19 16:25:46Z

2

Found a solution using then in keyword

function createActionType<K extends string>(...type: K[]): { [P in K]: string } {
    const actions = {};

    type.forEach((item: string) => {
        actions[item] = `${item}/${generateUniqueId()}`;
    });

    return Object.freeze(actions) as Readonly<{ [P in K]: string }>;
};

Using K as the arguments of the function, we can assign the return value to be an object with keys containing string literals defined by K.

Additional Reading: https://github.com/Microsoft/TypeScript/wiki/What's-new-in-TypeScript#mapped-types

edited Apr 19, 2017 at 16:25

answered Apr 10, 2017 at 23:39

dpaulus

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