how to check if variable is blank or undefined in node js

Question

I want to check my data is blank or undefined but my if block execute even my data is not blank ...

Code is :

router.post('/addNewGrade',function(req , res){ 
    var errorMsg = [];  
    console.log(req.body.gradeName)
    if(req.body.gradeName == '' || req.body.gradeName === undefined){
        errorMsg.push("please enter grade name");
    }
    if(req.body.gradeDescription == '' || req.body.gradeDescription === undefined){
        errorMsg.push("please enter description about your grade");
    }
    if(errorMsg !=''){
        res.send({errorMessage :errorMsg}); 
        return;
    }

});

what is the best way to check variable is undefined or not

Solution 1

Because an undefined variable is "falsey", you can simple do

if (body.req.gradeName) {
  // do normal stuff
} else {
  // do error stuff
}

Or if you don't need to do anything if it is defined, then you can do

if (!(body.req.gradeName)) {
 // do error stuff 
}

Solution 2

You can do it like this

if(typeof variable === 'undefined'){
//Variable isn't defined
}