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Re: Get inner text of HMTL element

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Cezary Tomczyk wrote:

> Thomas 'PointedEars' Lahn wrote:
>> Cezary Tomczyk wrote:
>>> [...]
>>> After longer research, experimenting and reading
>>> (http://www.kellegous.com/j/2013/02/27/innertext-vs-textcontent/) I
>>> think I can build something like this:
>>>
>>> var get_inner_text;
>>>
>>> if (typeof document.getElementsByTagName('html')[0].textContent ===
>>> 'string') {
>>
>> You should safely replace that with
>>
>>    if (typeof document.documentElement != "undefined"
>>        && typeof document.documentElement.textContent == "string")
>>    {
> 
> or
> 
> if (document.documentElement !== undefined && typeof
> document.documentElement.textContent === 'string') {

I wrote “safely” for a reason.  However,

  if (typeof document.documentElement != "undefined"
      && document.documentElement !== null
      && typeof document.documentElement.textContent == "string")
  {

should be even safer.

Since this is a common task, it is useful to define a general method that 
takes an object reference and a list of property names as arguments, whereas 
the property names specify the “path” of a property such that the property’s 
value can be obtained by repeated property access along that list:

  /**
   * Determines if a value refers to an object.
   *
   * <p>Returns <code>true</code> if the value is a reference
   * to an object; <code>false</code> otherwise.</p>
   *
   * <p>An value "is an object" if it is a function or
   * <code>typeof "object"</code> but not <code>null</code>.
   *
   * @return {boolean}
   */
  function _isObject (a)
  {
    var t = typeof a;
    return t == "function" || t == "object" && a !== null;
  }

  return {
    /**
     * Returns a feature of an object
     *
     * @param {Object} obj
     *   Object which provides the feature
     * @params {string}
     *   Property names on the feature path, including the property
     *   for the feature itself.  For example, use
     *   <code>jsx.object.getFeature("foo", "bar", "baz")</code> for
     *   safe access to <code>foo.bar.baz</code>.
     * @return {any}
     *   <code>undefined</code> if <var>obj</var> does not have such
     *   a feature.  Note that features whose value can be
     *   <code>undefined</code> cannot be detected with this method.
     */
    getFeature: function (obj) {
      for (var i = 1, len = arguments.length; i < len; i++)
      {
        var arg = arguments[i];
        if (_isObject(obj) && typeof obj[arg] != "undefined" && obj[arg])
        {
          obj = obj[arg];
        }
        else
        {
          return void 0;
        }
      }

      return obj;
    }
  };

See also: <http://PointedEars.de/wsvn/JSX/trunk/object.js>

A refined method would support specification of the property path as an 
Array of string values, and primitive false-values.  I am working on it.

>>>       get_inner_text = function(node) {
>>>           return node.textContent;
>>>       };
>>> } else if (document.createTreeWalker) {
>>
>> Insufficient and error-prone feature test for a host object's method, see
>> jsx.object.isHostMethod().
> 
> Yes, I know isHostMethod, but still I am feeling that it's not enough.
> Checking if host object is a function is one thing, but the second one
> if it's native or not. Once I had a scenario where trim() method was
> exists, but it was overwritten by some 3rd party library and this method
> wasn't working well. I've just realized it after some investigation :-(
> 
> However, last time I was thinking if it's strongly required every time
> for every scenario. As I remember:
> 
> 1. Some host objects in IE8 are as an "object", not a "function".
> 2. There is type "unknown", but it's related to only one case.
> 
> That's why I've been thinking that explicit conversion in that case is
> relatively safe.

Your logic is flawed.  It had been unrecoverable exceptions being thrown 
upon type-converting tests of host object's methods in MSHTML that prompted 
my/the creation of isMethod(), later isHostMethod(), in the first place.
 
>>>       get_inner_text = function(root) {
>>>           var w = document.createTreeWalker(root, 4, null, false),
>>>               result = '';
>>>            while (w.nextNode()) {
>>>                result += w.currentNode.data;
>>>            }
>>>            return result;
>>>       };
>>>
>>> } else {
>>
>> That the former two approaches fail does not mean that the third one must
>> work.
> 
> Hm, should I test if "firstChild" and "nextSibling" is supported before?
> Or do something else?

If you are to support “innerText” as well, *that* should be handled by the 
last branch.  Anyhow, there is no guarantee that if some arbitrary element 
object has a “firstChild” or “nextSibling” property, the *target* element 
object also has it.

Do you see now why it is a bad idea to infer from one property to another, 
even if the property names are the same and only the objects differ?
 
>>>       get_inner_text = function(node) {
>>>           var txt = '';
>>>
>>>           node = node.firstChild;
>>>           while (node) {
>>>               if (node.nodeType === 3 || node.nodeType === 4) {
>>
>> I avoid strict comparison against property values of host objects.  There
>> are too many unknowns.
> 
> I've never had problems with that, but I am not claim that there is no
> problems. However, if you have a time then provide maybe some valuable
> source where I can read about above problems. Otherwise, skip it, in
> case of having no time.

You are still operating in “Show me where it fails” mode in place of logic.
 
>>>               node = node.nextSibling;
>>>           }
>>>           return txt;
>>>       };
>>> }
>>>
>>> How about that?
>>
>> I do not think it is a good idea to infer from the existence of a
>> property on one (host) object the existence of a property of the same
>> name on another
> 
> Hm, is it then better to do in that way?
> 
> var get_inner_text = (function () {
> 
>      // here check what is available and return function
> 
> }());

No, same problem: The feature test does not happen on the target object 
because that object is not reliably accessible yet (if it even exists).
 
>> (host) object.  Therefore, I prefer approaches that test the properties
>> of the target object instead.
> 
> By "test" you mean using isHostMethod, isHostObjectProperty and
> isRealObjectProperty?

Yes, but not in the DM way, because that is error-prone even though it might 
be faster.
 
>> That aside, you should reconsider the actual probability that
>> Node::textContent (DOM Level 3) would not be implemented but
>> Document::createTreeWalker() (DOM Level 2 Traversal and Range) was.
> 
> Hm, maybe it is worth it to remove textContent and focus only on
> createTreeWalker or normal recursive iteration? Less code to maintenance.

And much less efficient with regard to runtime and memory.  You should as 
yourself instead whether there is any actual *need* for tree-walking at this 
point.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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Thread

Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-22 18:21 +0100
  Re: Get inner text of HMTL element Martin Honnen <mahotrash@yahoo.de> - 2014-02-22 19:31 +0100
    Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-22 20:51 +0100
      Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-22 21:11 +0100
        Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-22 21:37 +0100
          Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-22 22:05 +0100
            Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-22 23:38 +0100
              Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-23 10:43 +0100
                Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-23 14:50 +0100
                Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-23 15:48 +0100
                Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-24 21:01 +0100
                Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-24 22:34 +0100
                Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-27 21:41 +0100
                Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-27 22:32 +0100
                Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-28 13:44 +0100
                Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-28 16:54 +0100
                Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-03-04 20:51 +0100
                Re: Get inner text of HMTL element ompalompasales2@gmail.com - 2014-03-04 12:59 -0800
  Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-22 20:59 +0100
    Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-22 22:23 +0100
      Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-22 23:32 +0100
  Re: Get inner text of HMTL element Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-02-22 21:27 -0300
    Re: Get inner text of HMTL element "se" <se@no-one.here> - 2014-02-23 05:35 +0100
      Re: Get inner text of HMTL element Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-02-23 15:29 -0300
        Re: Get inner text of HMTL element "se" <se@no-one.here> - 2014-02-23 21:01 +0100
    Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-23 20:02 +0100
      Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-23 21:55 +0100
        Re: Get inner text of HMTL element Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2014-02-24 08:37 +0100
          Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-24 12:30 +0100
            Re: Get inner text of HMTL element Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-02-24 15:09 -0300
              Re: Get inner text of HMTL element Christoph Michael Becker <cmbecker69@arcor.de> - 2014-02-24 19:43 +0100
                Re: Get inner text of HMTL element Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-02-24 18:12 -0300
                Re: Get inner text of HMTL element Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-02-24 22:51 +0100
              Re: Get inner text of HMTL element Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-02-25 19:49 +0000
                Re: Get inner text of HMTL element Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-02-26 05:20 -0300
                Re: Get inner text of HMTL element "se" <se@no-one.here> - 2014-02-26 17:10 +0100
                OT - Re: Get inner text of HMTL element Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-02-26 15:48 -0300
                Re: OT - Re: Get inner text of HMTL element "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-02-26 22:43 +0100
                Re: OT - Re: Get inner text of HMTL element Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-02-27 15:00 +0000
                Re: OT - Re: Get inner text of HMTL element "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-02-28 10:50 +0100
                Re: OT - Re: Get inner text of HMTL element "se" <se@no-one.here> - 2014-02-27 10:57 +0100
                Re: Get inner text of HMTL element Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-02-27 15:46 +0000

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