users = users.map(x=> x.isPremium = true) :

Also, use let instead of const

You can use the function below to toggle any boolean value in your array.

function toggleBool(array, pram) {
  array.forEach(item => item[pram] = !item[pram]);
}

In this example you can do this:

toggleBool(users, 'isPremium')

Since all values are replacing without any condition, i have used _ in the map function to indicate the unused variable

let users = [{ isPremium: false },{ isPremium: false },{ isPremium: false }, { isPremium: false }, { isPremium: false }];
users = users.map(_=> ({'isPremium':true}));
console.log(users)

METHOD 2

Using forEach

var users = [{ isPremium: false },{ isPremium: false },{ isPremium: false }, { isPremium: false }, { isPremium: false }];
users.forEach((item) => item.isPremium = true);
console.log(users)

forEach: Iterates and transform the array and does not return anything.

map: This iterates over a array and returns another list of the same size with the transformed values.

METHOD 3

let users = [{ isPremium: false },{ isPremium: false },{ isPremium: false }, { isPremium: false }, { isPremium: false }];
users = JSON.parse(JSON.stringify(users).replaceAll("false","true"));
console.log(users)