Working with null and undefined in TypeScript

TypeScript Basic: Exercise-10 with Solution

Write a TypeScript program that declares a variable 'isNull' and assigns it null. You should also declare a variable called 'isUndefined' and assign it an undefined value.

Sample Solution:

TypeScript Code:

// Declare a variable 'isNull' and assign it null
let isNull: null = null;

// Declare a variable 'isUndefined' and assign it undefined
let isUndefined: undefined = undefined;

// Print the values of the variables
console.log("isNull:", isNull);
console.log("isUndefined:", isUndefined);

Explanations:

In the exercise above -

• First we declare a variable 'isNull' and explicitly specify its type as 'null' by using the type annotation: null. This means that 'isNull' can only hold the value 'null'.
• Next we declare a variable 'isUndefined' and explicitly specify its type as 'undefined' using the type annotation : undefined. This means that 'isUndefined' can only hold the value 'undefined'.
• Finally we use console.log to print the values of 'isNull' and 'isUndefined' to the console.

Output:

"isNull:"
null
"isUndefined:"
undefined

TypeScript Editor:

See the Pen TypeScript by w3resource (@w3resource) on CodePen.

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