Is there a way to check for both `null` and `undefined`?

Question

Since TypeScript is strongly-typed, simply using if () {} to check for null and undefined doesn't sound right.

Does TypeScript have any dedicated function or syntax sugar for this?

Answer 1

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

if (x == 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 (x === null) { 

You can try this with various values using this example:

var a: number; var b: number = null;  function check(x, name) {     if (x == null) {         console.log(name + ' == null');     }      if (x === null) {         console.log(name + ' === null');     }      if (typeof x === 'undefined') {         console.log(name + ' is undefined');     } }  check(a, 'a'); check(b, 'b'); 

Output

"a == null"

"a is undefined"

"b == null"

"b === null"

Answer 2

if( value ) { } 

will evaluate to true if value is not:

• null
• undefined
• NaN
• empty string ''
• 0
• false

typescript includes javascript rules.