How to check for an undefined or null variable in JavaScript?

Question

We are frequently using the following code pattern in our JavaScript code

if (typeof(some_variable) != \'undefined\' && some_variable != null)
{
             


        

Answer 1

If the purpose of the if statement is to check for null or undefined values before assigning a value to a variable, you can make use of the Nullish Coalescing Operator, is finally available on JavaScript, though browser support is limited. According to the data from caniuse, only 48.34% of browsers are supported (as of April 2020).

const a = some_variable ?? '';

This will ensure that the variable will be assigned to an empty string (or any other default value) if some_variable is null or undefined.

This operator is most suited for your use case, as it does not return the default value for other types of falsy value such as 0 and ''.