undefined and null in JavaScript Explained

undefined and null in JavaScript Explained

undefined and null are two data types in JavaScript that can sometimes be confusing. This tutorial will help you learn about them. It will explain what undefined and null in JavaScript are. You will also learn what are some differences between these two and how to work with them.

undefined and null are two data types in JavaScript that can sometimes be confusing. This tutorial will help you learn about them. It will explain what undefined and null in JavaScript are. You will also learn what are some differences between these two and how to work with them.

The basics

Both, undefined and null, are primitive data types that exist in JavaScript. These data types are Boolean, Number, String, Symbol, Null and Undefined. The rest of values in JavaScript are objects. Another thing undefined and null have in common is that they are both falsy values.

This means that when you use undefined in a boolean context it will be considered false. Boolean context is a context which evaluates to boolean value, either true or false. One example of boolean context is condition in if…else statement. This is also why you should avoid testing for loose equality.

When you test for loose equality there is type coercion happening on the background. Both, undefined and null, are falsy and this is what they will be considered. The result of test for loose equality will result in match. The result of this test will be true. However, this is not really correct.

These two data types are not the same. If you want to avoid many problems, avoid testing for loose equality. Instead of loose equality, test for strict equality. When you test for strict equality JavaScript doesn’t perform type coercion. Strict check will compare not only the value but also the data type.

undefined and null in JavaScript are different data types. This means that strict equality test will tell you, correctly, that these two are not the same.

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