How to check undefined in Typescript

Question

I am using this code to check undefined variable but it\'s not working.

Answer 1

Adding this late answer to check for object.propertie that can help in some cases:

Using a juggling-check, you can test both null and undefined in one hit:

if (object.property == null) {

If you use a strict-check, it will only be true for values set to null and won't evaluate as true for undefined variables:

if (object.property === null) {

Typescript does NOT have a function to check if a variable is defined.

Update October 2020

You can now also use the nullish coallesing operator introduced in Typescript.

let neverNullOrUndefined = someValue ?? anotherValue;

Here, anotherValue will only be returned if someValue is null or undefined.