JavaScript Set Default Value on Function Not Working?

Question

Function in JS

    function punch(){
    var a,b,result;
    a=document.getElementById('n1').value;
    b=document.getElementById('n2').value;

    var x=parseInt(a);
    var y=parseInt(b);
    result=x+y;


     if (result===NaN)
     result =0;

I know this condtition is false and it gives output of x+y. On empty fields it always return NaN value when change it to

if (result!==NaN)
 result=0;

Now it becomes true but it gives x+y also 0.

document.getElementById('n3').value=result;   
}

HTML Code

<input type="text" id="n1" placeholder="Value 1"/>
<input type="text" id="n2" placeholder="Value 2"/>
<button type="button" onClick="punch()">Click For Answer</button>
<input type="text" id="n3" placeholder="Answer"/>

Pointy · Accepted Answer · 2015-05-07 19:57:01Z

1

Nothing, including NaN, is ever === to NaN. In fact one way to test for NaN is to exploit that!

if (result !== result)
  result = 0; // must have been NaN!

You can also use isNaN():

if (isNaN(result))
  result = 0;

answered May 7, 2015 at 19:57

Pointy

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2 Comments

Pointy Over a year ago

@DontVoteMeDown yes I would use that preferentially; the first is just for illustration (though I've seen it used).

Ven Nilson Over a year ago

Pointy Thanks for help! just play little bit with variable (result !== result) and its become true

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