The value to check.
// Basic usage
isDef(0); // => true
isDef(null); // => true
isDef(''); // => true
isDef(undefined); // => false
// Using as a type guard to filter an array
const values = [1, 2, undefined, 3, undefined];
const definedValues = values.filter(isDef);
// definedValues is now [1, 2, 3]
// and its type has been narrowed to number[]
Checks if the provided value is defined This is a type-safe equivalent to
x !== undefined.