JavaScript Program To Check If A Variable Is undefined or null

// program to check if a variable is undefined or null

function checkVariable(variable) {

    if(variable == null) {
        console.log('The variable is undefined or null');
    }
    else {
       console.log('The variable is neither undefined nor null');
    }
}

let newVariable;

checkVariable(5);
checkVariable('hello');
checkVariable(null);
checkVariable(newVariable);

Output

The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is undefined or null
The variable is undefined or null