In Javascript. how can I tell if a field exists inside an object?

Question

And of course I want to do this code-wise. It\'s not that there isn\'t alternative to this problem I\'m facing, just curious.

Answer 1

In addition to the above, you can use following way:

if(obj.myProperty !== undefined) {
}

Answer 2

UPDATE: use the hasOwnProperty method as Gary Chambers suggests. The solution below will work, but it's considered best practice to use hasOwnProperty.

if ('field' in obj) {
}

Answer 3

This will ignore attributes passed down through the prototype chain.

if(obj.hasOwnProperty('field'))
{
    // Do something
}

Answer 4

After much frustration trying to test a field name which is passed via a variable, I came up with this:

`function isset(fName){ 
    try{
        document.getElementById(fName).value=document.getElementById(fName).value;  
        return true;
    }catch(err){
        return false;
    }
 }

`

The function uses the try/catch function of javascript - if it can't set the field value it will trigger an error which is caught and passed back as false, otherwise true is returned.

Answer 5

There is has method in lodash library for this. It can even check for nested fields.

_.has(object, 'a');     
_.has(object, 'a.b');