How to check if a Variable Is Not Null in JavaScript ?
You can easily check if a variable Is Null or Not Null in JavaScript by applying a simple if-else condition to the given variable.
There are two ways to check if a variable is null or not. First I will discuss the wrong way that seems to be right to you at first, then we will discuss the correct way to check if a variable is null or not.
Method 1: The wrong way seems to be right.
Condition:
if(my_var) {
....
}
Note: When a variable is null, there is an absence of any object value in a variable. Null is often retrieved in a place where an object can be expected, but no object is relevant.
By the above condition, if my_var is null then the given if condition will not execute because null is a falsy value in JavaScript, but in JavaScript, there are many pre-defined falsy values like
- undefined
- null
- 0
- “” ( empty string)
- false
- NaN
So if my_var is equal to any of the above pre-defined falsy values then if the condition would not execute or vice-versa.
Example: This example shows the use of the above-explained approach.
HTML
<!DOCTYPE html><html lang="en"><head> <title> How to check if a Variable Is Not Null in JavaScript ? </title></head><body> <h2 style="color:green;"> GeeksforGeeks </h2> <p> variable-name : GFG_Var </p> <button onclick="myGeeks()"> Check for vowel </button> <h3 id="div" style="color:green;">HTML</h3> <!-- Script to check existence of variable --> <script> function myGeeks() { var h3 = document.getElementById("div"); var GFG_Var = h3.innerHTML; // check if GFG_Var variable contain any vowels // HTML text contains no vowels, // so variable my_var will be assigned null const my_var = GFG_Var.match(/[aeiou]/gi); if (my_var) { h3.innerHTML = "Variable is not null"; } else { h3.innerHTML = "Variable is NULL"; } } </script></body></html> |
Output:
Check for vowel
Method 2: The following code shows the correct way to check if the variable is null or not.
Condition:
if(my_var !== null)
{
....
}
The above condition is actually the correct way to check if a variable is null or not. The if condition will execute if my_var is any value other than a null i.e
- If my_var is undefined then the condition will execute.
- If my_var is 0 then the condition will execute.
- If my_var is ” (empty string) then the condition will execute.
- …
This condition will check the exact value of the variable whether it is null or not.
Example: This example shows the use of the above-explained approach.
HTML
<!DOCTYPE html><html lang="en"><head> <title> How to check if a Variable Is Not Null in JavaScript ? </title></head><body> <h2 style="color:green;"> GeeksforGeeks </h2> <p> variable-name : GFG_Var </p> <button onclick="myGeeks()"> Check for vowel </button> <h3 id="div" style="color:green;">HTML</h3> <!-- Script to check existence of variable --> <script> function myGeeks() { var h3 = document.getElementById("div"); var GFG_Var = h3.innerHTML; // check if GFG_Var variable contain any vowels // HTML text contain no vowels // so variable my_var will assign null const my_var = GFG_Var.match(/[aeiou]/gi); // this will check exactly whether variable is null or not if (my_var !== null) { h3.innerHTML = "Variable is not null"; } else { h3.innerHTML = "Variable is NULL"; } } </script></body></html> |
Output: The output is the same as in the first example but with the proper condition in the JavaScript code.
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