I have flagged enum below
enum PermissionEnum {
SU = 1 << 0, // 1
Administrator = 1 << 1, // 2
User = 1 << 2 // 4
}
For given value 6, how can I get
string[] -> ['Administrator', 'User']
number[] -> [2,4]
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2 Answers
You can add a static function into the enum namespace and use that to do the conversion.
Also you can use a trick to extract the set bits from a number without having to iterate over all the unset ones: n & (~n+1) gives you the lowest set bit.
enum PermissionEnum {
SU = 1 << 0, // 1
Administrator = 1 << 1, // 2
User = 1 << 2 // 4
}
namespace PermissionEnum {
export function toValues(n: PermissionEnum) {
const values: string[] = [];
while (n) {
const bit = n & (~n+1);
values.push(PermissionEnum[bit]);
n ^= bit;
}
return values;
}
}
console.log(PermissionEnum.toValues(PermissionEnum.Administrator));
console.log(PermissionEnum.toValues(PermissionEnum.Administrator + PermissionEnum.SU));
Output is:
[ 'Administrator' ]
[ 'SU', 'Administrator' ]
The conversion to numbers would be the same but just pushing bit without a lookup.
Comments
That should work:
let x: PermissionEnum = PermissionEnum.Administrator | PermissionEnum.User;
const permNum: number[] = [];
const permStr: string[] = [];
let i = 0;
let perm: number;
while (PermissionEnum[perm = 1 << i++]) {
if (x & perm) {
permNum.push(perm);
permStr.push(PermissionEnum[perm]);
}
}
