CODEWITHSUNDEEP
javascriptnode.js
Jonas Sciangula Street
Jonas Sciangula Street

Reputation: 1892

Javascript - Detecting defined variable as undefined

For example:

var myObj = {
    yes: undefined
}

console.log(typeof myObj.yes === 'undefined') //--> true
console.log(typeof myObj.nop === 'undefined') //--> true too

Is there a way to detect if myObj.nop is not defined as undefined ?

Upvotes: 2

Views: 80

Answers (3)

vivek
vivek

Reputation: 1605

var myObj = {
    yes: undefined
}

console.log( myObj.yes === undefined); // gives true

and 

var myObj = {
        yes: 'any value here'
    }

    console.log( myObj.yes === undefined); // gives false

One thing to note here is that the undefined is not in single quotes. May be this gives you right direction.

Upvotes: 0

Don Rhummy
Don Rhummy

Reputation: 25820

Use hasOwnProperty.

myObj.hasOwnProperty('yes');             // returns true
myObj.hasOwnProperty('nop');         // returns false

Upvotes: 1

Josh Beam
Josh Beam

Reputation: 19772

You would use in:

if('yes' in myObj) {
  // then we know the key exists, even if its value is undefined
}

Keep in mind, this also checks for properties in the object's prototype, which is probably fine in your case, but in case you only want to check properties that are directly set on that specific object, you can use Object.prototype.hasOwnProperty:

if(myObj.hasOwnProperty('yes')) {
  // then it exists on that object
}

Here's a good article on the difference between the two.

Upvotes: 5

Related Questions