typescript declaring null
interface Employee1 { name: string; salary: number; } var a: Employee1 = { name: 'Bob', salary: 40000 }; // OK var b: Employee1 = { name: 'Bob' }; // Not OK, you must have 'salary' var c: Employee1 = { name: 'Bob', salary: undefined }; // OK var d: Employee1 = { name: null, salary: undefined }; // OK // OK class SomeEmployeeA implements Employee1 { public name = 'Bob'; public salary = 40000; } // Not OK: Must have 'salary' class SomeEmployeeB implements Employee1 { public name: string; }
Source: stackoverflow.com