Why does eval() give undefined value in Javascript?

Question

I am working in JavaScript coding. I have created a text area with name OQ_0 and value "0". When i use eval() method for that field in JavaScript it is giving the value undefined. The below are the part of JavaScript code

var tempOpenQtyStr = "document.InitiateReturnsForm.OQ" + "_" + 0; 
var tempOpenxQtyStr = eval(tempOpenQtyStr).value;
alert('Manuals =' + document.InitiateReturnsForm.OQ_0.value);
alert('eval(tempOpenxQtyStr ) =' + eval(tempOpenxQtyStr));
alert('eval(tempOpenxQtyStr).value =' + eval(tempOpenxQtyStr).value);

Output:

Manuals = 0
eval(tempOpenxQtyStr ) = 0 --- Here it is suppose to show "[object]"
eval(tempOpenxQtyStr).value = undefined.

Kindly help me out what is change to do. Thanks in advance.

Could you please post the html part relating to this, just so that we can see the DOM, Thanks — Mahesh Velaga
– Mahesh Velaga, Commented Mar 10, 2010 at 12:50

Ignacio Vazquez-Abrams · Accepted Answer · 2010-03-10 12:50:00Z

5

Why not just use document.InitiateReturnsForm["OQ_" + 0].value?

answered Mar 10, 2010 at 12:50

Ignacio Vazquez-Abrams

804k160 gold badges1.4k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Phil Ross · Accepted Answer · 2010-03-10 12:53:56Z

1

Try

alert('eval(tempOpenxQtyStr ) = ' + eval(tempOpenQtyStr));
alert('eval(tempOpenxQtyStr).value = ' + eval(tempOpenQtyStr).value);

In the second and third alert you are evaluating the second variable which stores the value of the first evaluated object. That's why the error occurs.

edited Mar 10, 2010 at 12:53

Phil Ross

26.2k9 gold badges71 silver badges80 bronze badges

answered Mar 10, 2010 at 12:50

rahul

188k50 gold badges239 silver badges266 bronze badges

Comments

Oskarols · Accepted Answer · 2010-03-10 13:36:22Z

1

alert('eval(tempOpenxQtyStr ) =' + eval(tempOpenxQtyStr));

Since you put a string, not an object, inside tempOpenxQtyStr, it evaluates that string and returns 0.

alert('eval(tempOpenxQtyStr).value =' + eval(tempOpenxQtyStr).value);

Here you're using a method on a variable that contains a string. That doesn't work. It doesn't have that method, that's why it returns undefinied.

You might want to try doing eval(tempOpenxQtyStr.value) instead of eval(tempOpenxQtyStr).value since the last one does basically nothing, just evaluating an object and then fetching the objects value (it doesn't eval the value itself).

edited Mar 10, 2010 at 13:36

answered Mar 10, 2010 at 13:30

Oskarols

315 bronze badges

Collectives™ on Stack Overflow

Why does eval() give undefined value in Javascript?

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related