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Global variable is deletable?

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  Global variable is deletable? Thomas Li <cooooooder@gmail.com> - 2013-01-07 01:21 -0800
    Re: Global variable is deletable? Stefan Weiss <krewecherl@gmail.com> - 2013-01-07 11:24 +0100
      Re: Global variable is deletable? JJ <jaejunks@nah.meh> - 2013-01-07 15:36 +0000
        Re: Global variable is deletable? Scott Sauyet <scott.sauyet@gmail.com> - 2013-01-07 07:50 -0800
      Re: Global variable is deletable? Thomas Li <cooooooder@gmail.com> - 2013-01-07 22:08 -0800
    Re: Global variable is deletable? dann90038@gmail.com - 2013-01-07 13:25 -0800
      Re: Global variable is deletable? Thomas Li <cooooooder@gmail.com> - 2013-01-07 21:48 -0800

#17999 — Global variable is deletable?

Hi, I'm fresh in Javascript. From the book "Javascript, the definitive guide", the global variable should be nondeletable, however when I test it in IE, it is deletable, anything wrong? 
Steps:
1. Open IE 9
2. Press F12 and select Console panel
3. Var temp = 1;
   delete temp;
4. it returns true and when I enter temp, it says "temp is undefined"

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#18001

On 2013-01-07 10:21, Thomas Li wrote:
> Hi, I'm fresh in Javascript. From the book "Javascript, the
> definitive guide", the global variable should be nondeletable,
> however when I test it in IE, it is deletable, anything wrong? 
> Steps:
> 1. Open IE 9
> 2. Press F12 and select Console panel
> 3. Var temp = 1;
>    delete temp;
> 4. it returns true and when I enter temp, it says "temp is undefined"

When you enter something in the console, it gets evaluated with eval().
Variables created from eval()ed code don't have the DontDelete flag set.

Details:
http://perfectionkills.com/understanding-delete/#firebug_confusion


- stefan

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#18008

Stefan Weiss <krewecherl@gmail.com> wrote:
> On 2013-01-07 10:21, Thomas Li wrote:
>> Hi, I'm fresh in Javascript. From the book "Javascript, the
>> definitive guide", the global variable should be nondeletable,
>> however when I test it in IE, it is deletable, anything wrong? 
>> Steps:
>> 1. Open IE 9
>> 2. Press F12 and select Console panel
>> 3. Var temp = 1;
>>    delete temp;
>> 4. it returns true and when I enter temp, it says "temp is undefined"
> 
> When you enter something in the console, it gets evaluated with eval().
> Variables created from eval()ed code don't have the DontDelete flag 
set.
> 
> Details:
> http://perfectionkills.com/understanding-delete/#firebug_confusion
> 
> 
> - stefan

I'd toss that book.

<!DOCTYPE html>
<html>
<body>
<script>
console.log(typeof abc); //undefined
abc=123;
console.log(typeof abc); //number
delete abc;
console.log(typeof abc); //undefined
</script>
</body>
</html>

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#18009

JJ wrote:
> Stefan Weiss wrote:
>> On 2013-01-07 10:21, Thomas Li wrote:
>>> Hi, I'm fresh in Javascript. From the book "Javascript, the
>>> definitive guide", the global variable should be nondeletable,
>>> however when I test it in IE, it is deletable, anything wrong?
>>> Steps:
>>> 1. Open IE 9
>>> 2. Press F12 and select Console panel
>>> 3. Var temp = 1;
>>>    delete temp;
>>> 4. it returns true and when I enter temp, it says "temp is undefined"
>
>> When you enter something in the console, it gets evaluated with eval().
>> Variables created from eval()ed code don't have the DontDelete flag
>> set.
>
>> Details:
>> http://perfectionkills.com/understanding-delete/#firebug_confusion

> I'd toss that book.
>
> <!DOCTYPE html>
> <html>
> <body>
> <script>
> console.log(typeof abc); //undefined
> abc=123;
> console.log(typeof abc); //number
> delete abc;
> console.log(typeof abc); //undefined
> </script>
> </body>
> </html>

Back away from the trash can with that book!

Undeclared assignment does not set the DontDelete attribute.  If you'd
read the article Stefan mentioned, I'm sure you would have seen that.
(I'm not going to re-read it now to find out where, but I'm pretty
sure that kangax's article is where I learned it in the first place.)

    console.log(typeof abc); //undefined
    var abc = 123;
//  ^^^
    console.log(typeof abc); //number
    delete abc; // false
    console.log(typeof abc); //number

  -- Scott

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#18017

On Monday, January 7, 2013 6:24:10 PM UTC+8, Stefan Weiss wrote:
> On 2013-01-07 10:21, Thomas Li wrote:
> 
> > Hi, I'm fresh in Javascript. From the book "Javascript, the
> 
> > definitive guide", the global variable should be nondeletable,
> 
> > however when I test it in IE, it is deletable, anything wrong? 
> 
> > Steps:
> 
> > 1. Open IE 9
> 
> > 2. Press F12 and select Console panel
> 
> > 3. Var temp = 1;
> 
> >    delete temp;
> 
> > 4. it returns true and when I enter temp, it says "temp is undefined"
> 
> 
> 
> When you enter something in the console, it gets evaluated with eval().
> 
> Variables created from eval()ed code don't have the DontDelete flag set.
> 
> 
> 
> Details:
> 
> http://perfectionkills.com/understanding-delete/#firebug_confusion
> 
> 
> 
> 
> 
> - stefan

Great thanks and the reference is very helpful

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#18010

-> Thomas Li

I have JS Definitive Guide 5th edition, on chapter 4.2 as you read on the last paragraph of that section:
-----------------------------
Variables declared with var are permanent: attempting to delete them with the delete operator causes an error. (The delete operator is introduced in Chapter 5.)
-----------------------------

I gather you misunderstood the statement.  The paragraph refers to the limits the 'delete' operator capability, as you could see at -> http://www.webdevout.net/test?016&raw

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#18015

On Tuesday, January 8, 2013 5:25:57 AM UTC+8, dann...@gmail.com wrote:
> -> Thomas Li
> 
> 
> 
> I have JS Definitive Guide 5th edition, on chapter 4.2 as you read on the last paragraph of that section:
> 
> -----------------------------
> 
> Variables declared with var are permanent: attempting to delete them with the delete operator causes an error. (The delete operator is introduced in Chapter 5.)
> 
> -----------------------------
> 
> 
> 
> I gather you misunderstood the statement.  The paragraph refers to the limits the 'delete' operator capability, as you could see at -> http://www.webdevout.net/test?016&raw

Great thanks for your help :)

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