Telling the differences between null and undefined can be tricky. Testing these with if statements will give us the same result, false. What’s the difference between one and the other?
null
Something set on purpose to say that there is nothing there. It means just nothing, emptiness. Type of null is object. Indicates the absence of a value.
We can use null as a value when we want to create a new variable and just not use it at the beginning. For example we want to use it later in our code, but we need to have the variable already created.
undefined
Something that does not have a value, but it's container exists. Type of undefined is undefined. Indicates absence of variable itself.
//
var name;
console.log(name); //undefined
function sayHello() {
//if function body will be empty then function will return undefined
}
sayHello(); //undefined
Console logs in action with null and undefined
Below you will find examples of the use and comparison of null and undefined.
// console.log(typeof null); //object console.log(typeof undefined); //undefined console.log(!undefined); //true console.log(!null); //true console.log(undefined == undefined); //true console.log(undefined === undefined); //true console.log(null == null); //true console.log(null === null); //true console.log(null == undefined); //true console.log(null === undefined); //false //
The last two cases are interesting. When we compare null to undefined with == it will compare only the value, and the value will be false for both null and undefined. But when we compare null to undefined with === (it also compares the type) then the result will be false because type of null is an object and type of undefined is undefined.