Check null and undefined in javascript

They behave in a very strange and many general rules do not apply to them. Before deep-diving into their strange behavior, let's first understand what null and undefined is.

The meaning of undefined is "no value assigned". If a variable is declared but not assigned then its value is undefined. However, explicitly assigning undefined to a variable is not recommended. It is a bad code practice. Hence, you can check the undefined value using typeof operator.

Note : We cannot use the typeof operator for null as it returns object. Course Index Explore Programiz. Popular Tutorials Operators in JavaScript. JavaScript for Loop. Functions in JavaScript. JavaScript Objects. Arrays in JavaScript. As we have seen in the variable section that we can assign any primitive or non-primitive type of value to a variable. JavaScript includes two additional primitive type values - null and undefined, that can be assigned to a variable that has special meaning.

You can assign null to a variable to denote that currently that variable does not have any value but it will have later on. A null means absence of a value. In the above example, null is assigned to a variable myVar. It means we have defined a variable but have not assigned any value yet, so value is absence. If you try to find DOM element using document.

So it is recommended to check for null before doing something with that element. How to check undefined null value in Javascript? May 23, Many times you are given APIs in which the response is not constant. In such situation, you need to check for undefined and null values. Before jumping onto the important part.

Let's first understand. A falsy sometimes written falsey value is a value that is considered false when encountered in a Boolean context. Falsy values when coerced in Javascript's Engine into a boolean value evaluate as false , but they are not necessarily equal to each other.

This one is the easiest and the lengthiest at the same time. In this method, we have created a function checkUndefinedNull which checks the undefined and null.