JavaScript Comparing undefined value in JavaScript

I have an object whose value may be undefined sometimes. So is it possible / valid / good practice to test it with an if case like below :

if(params === undefined)  
{  
    alert("sound." + params);  
}  

If not, why can't we do it?

As of now, it is working fine. Yet, I would like to know if it can go wrong anytime?

Thanks

Answer:1

Use typeof varName for safer usage:-

This will not throw any error if params is not a variable declared anywhere in your code.

 if(typeof params  === "undefined")
   {
       //it is not defined
   }

 if(params === undefined)   //<-- This will fail of you have not declared the variable 
        //param. with error "Uncaught ReferenceError: params is not defined "
 {
 }

Refer Undefined

Answer:2

Since in theory undefined can be redefined (at least pre-JS 1.8.5), it's better to use

if (typeof params === 'undefined')

This also works without throwing an error if params is not a known variable name.

Answer:3

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