Function isUndefined

isUndefined<T>(this: void, x: T | undefined): x is undefined
Verifies that the given value is undefined. This especially helps with a .filter
Type Parameters
- T
Parameters
- this: void
- x: T | undefined
Returns x is undefined
Example
```
const values: (number | undefined)[] = [1, 2, undefined, 4];
const undefinedValues: undefined[] = values.filter(isUndefined);
// undefinedValues is now of type undefined[]
```
See
- isNotUndefined
- isNotNull
- Defined in src/util/assert.ts:52