How to handle both a single item and an array of string type in javascript / typescript

Question

I get response from an api regarding user roles, if user has one role, I get single value place holder ie

    {
  "nameid": "1",
  "unique_name": "Anees",
  "role": "Student",
  "nbf": 1587681052,
  "exp": 1587767452,
  "iat": 1587681052
}

If user has more than one roles, roles consider as array ie.

    {
  "nameid": "2",
  "unique_name": "Naveed",
  "role": [
    "SuperAdmin",
    "Admin",
    "Teacher",
    "Clerk",
    "Student"
  ],
  "nbf": 1587712850,
  "exp": 1587799250,
  "iat": 1587712850
}

How can I handle both a single value and a collection in same place holder?

This script work fit for me

const userRoles = this.decodedToken.role as Array<string>;

I have to use some collection methods like find etc

var status = userRoles.find(x => x == role);

it gives error in case of single value.

Any solution, please.

Answer 1

You could convert the single item to an array containing single element. Check if the element is an array using Array.isArray() function. Try the following

const userRoles = Array.isArray(this.decodedToken.role) ? this.decodedToken.role : [this.decodedToken.role];

let status = userRoles.find(x => x == role);

As a sidenote, using let instead of var helps to keep things the Typescript way.

Answer 2

Casting will always succeed, so you need to check the type at runtime.

You can check to see if the value is an array using isArray

const isRolesArray = Array.isArray(userRoles)

var status = isRolesArray ? userRoles.find(x => x == role) : userRoles === role;

Or you can cast to the proper typescript type using union types and do a check using type guards . So you can do something like this

const userRoles = this.decodedToken.role as Array<string> | string;

let status

if (typeof userRoles === "string") {
 status = userRoles === role
} else {
 status = userRoles.find(x => x == role);
}

This way you get all the typechecking goodness from Typescript.

Answer 3

you can use something like this. Array.isArray() can easily check this

//declares a variable for object

let newobject = {
 "nameid": "2",
 "unique_name": "Naveed",
 "role": [
 "SuperAdmin",
 "Admin",
 "Teacher",
 "Clerk",
 "Student"
 ],
"nbf": 1587712850,
"exp": 1587799250,
"iat": 1587712850
}
function t(arr){
 let status;
 if(Array.isArray(arr)){
  status = arr.find(x => x == "Admin");
 } else {
  status = newobject.role;
 }
console.log('status ',status);
}
t(newobject.role); //call this for activating the check