Typescript: enum keys as parameter to function

Question

I have this enum

enum methods {
  DELETE = 1,
  POST,
  PUT,
  GET
}

I want to have a function accepting a parameter that can be one of the keys of the methods enum.

const getMethodPriority = (method /* how do I type this? */) => {
  return methods[method];
};

so, for example getMethodPriority("DELETE") would return 1.

How do I type the method parameter?

You can go with (method: keyof typeof methods)

Aleksey L.
– Aleksey L.

2018-02-20 07:46:41 +00:00
Commented Feb 20, 2018 at 7:46 — Aleksey L.
– Aleksey L., Commented Feb 20, 2018 at 7:46

Pavel Agarkov · Accepted Answer · 2018-02-20 18:18:06Z

12

You can directly obtain numbers from numeric enums by converting their values to number:

enum methods {
    DELETE = 1,
    POST = 2,
    PUT = 3,
    GET = 4
}

let enumPriority = methods.DELETE as number;
// enumPriority == 1

But if you really want to have a method for this you can:

enum methods {
    DELETE = 1,
    POST = 2,
    PUT = 3,
    GET = 4
}

const getMethodPriority = (method: keyof typeof methods) => {
    return methods[method];
};

// how to call
getMethodPriority("DELETE");

edited Feb 20, 2018 at 18:18

answered Feb 19, 2018 at 20:57

Pavel Agarkov

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3 Comments

Emilios1995 Over a year ago

Sorry!! methodPriorities was supposed to be just methods. please see my updated getMethodPriority function

Pavel Agarkov Over a year ago

if so - you don't need any function - just convert to number as I wrote in PS section.

bsplosion Over a year ago

As an added bonus of using the keyof typeof combination, you can also do type checking of compound enums, such as a dot-separated path string that gets unpacked later like 'property.subprop.field' - that's not possible with a direct enum reference.

Jeff Lau · Accepted Answer · 2018-02-24 05:41:57Z

0

Use the keyof and typeof operators like this:

enum methods {
  DELETE = 1,
  POST,
  PUT,
  GET
}

const getMethodPriority = (method: keyof typeof methods) => {
    return methods[method];
};

answered Feb 24, 2018 at 5:41

Jeff Lau

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