undefined are used to represent the absence of a value or a placeholder for an unknown value. It is important to understand the differences between these two values, as they can behave differently in certain situations.
In this article, we will examine the concepts of
# Differences between
The first thing to note is that
undefined are not the same value.
null is a special value that represents the absence of an object reference, while
undefined is a primitive value that represents the absence of a value or the default value of an uninitialized variable.
One of the main differences between
undefined is how they behave when compared using the equality operators
The loose equality
== operator performs a type coercion, meaning that it converts the operands to the same type before making the comparison. This means that
null == undefined is
true, because both values are considered to be “falsy” and are therefore coerced to
0 when compared.
# Strict equality
On the other hand, the strict equality
=== operator performs a strict comparison, meaning that it does not perform type coercion. This means that
null === undefined is
false, because the operands have different types.
It is generally recommended to use the
However, there are some situations where using the
=== operator may be necessary, such as when comparing values that may be either
undefined. In these cases, it is important to understand how the operator behaves and to use it appropriately.
undefined. For example, the
+ operator will convert
0 when used in an arithmetic expression, while the
typeof operator will return “object” for
null and “undefined” for
Overall, it is important to be aware of the differences between