By using a juggling-check, we can check both null and undefined :
if (x == null) {
} ​
If we use a strict-check, it will always true for values set to null and won't evaluate as true for undefined variables.
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"
