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Re: Object.defineProperties

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On 08/05/2017 00:50, Stefan Weiss wrote:
> Cezary Tomczyk wrote:
>> So, Object.assign does shallow copy, not deep copy. My goal , by having
>> "extend" function in that case, is to do deep copy.
>>
>> If I do extend({}, o); then new object will have his own data and changes
>> made on new object must not reflect on the source object.
>
> Okay, that makes sense. I thought you were saying that the action of
> Object.assign() itself caused the source object to be modified.
>
>>     function extend(target, source) {
>>         var output = target;
>>
>>         function processProperty(key) {
>>             if (isTypeOf(source[key], 'object')) {
>>                 output[key] = {};
>>                 extend(output[key], source[key]);
>>             } else if (isTypeOf(source[key], 'array')) {
>>                 output[key] = source[key].slice(0);
>>             } else {
>>                 output[key] = source[key];
>>             }
>>         }
>>
>>         Object.keys(source).forEach(processProperty);
>>
>>         return output;
>>     }
>
> Without testing this myself, I can see a potential problem: an array in the
> source object could contain objects as elements. Your extend() function does
> a shallow copy on arrays, so modifying objects in the target array will
> affect both the source and the target.

Since my last post I rewrote it to:

     function extend(destination, source) {
         var property,
             src;

         function cloneArray(a) {
             return Object.assign({}, a);
         }

         for (property in source) {

             if (Object.prototype.hasOwnProperty.call(source, property)) {
                 src = source[property];

                 if (isTypeOf(src, 'object')) {
                     destination[property] = destination[property] || {};
                     extend(destination[property], src);
                 } else if (Array.isArray(src)) {
                     destination[property] = src.map(cloneArray);
                 } else if (getTypeOf(src) === 'date') {
                     destination[property] = new Date(src.valueOf());
                 } else if (getTypeOf(src) === 'regexp') {
                     destination[property] = new RegExp(src);
                 } else {
                     destination[property] = source[property];
                 }
             }

         }
         return destination;
     }

Of course, this doesn't cover all scenarios, but at least some major 
cases that I need.

> Apart from that, I still don't quite see the use for the isTypeOf()
> function... what's wrong with this:
>
>     if (Array.isArray(source[key])) {
>         // clone array (and recurse)
>     } else if (typeof source[key] == "object" && source[key] !== null) {
>         // clone object (and recurse)
>     } else {
>         // copy scalar values (and null)
>     }

There are even more cases that I've discovered while writing unit tests. 
I gave up and simplified to:

     var _toString = {}.toString;

     function getTypeOf(obj) {
         if (arguments.length !== 1) {
             return false;
         }

         return _toString.call(obj).slice(8, -1).toLowerCase();
     }

     function isTypeOf(obj, typeToCheck) {
         var type;

         if (arguments.length < 2) {
             throw new TypeError('[isTypeOf] requires two arguments'); 
// The error message will have more precise data as Thomas suggested
         }

         type = typeToCheck.toLowerCase();

         return getTypeOf(obj) === type;
     }

> For the sake of completeness, I'd like to amend my earlier statement:
> The `typeof` operator, `Array.isArray()`, *and strict comparisons* are
> usually all that's needed.

This would not be enough. For example, if you do typeof Date or RegExp 
object you will get "object" in result. And that is not what I want. 
Because of that I think using "toString" here is fine. Even, if there 
are edge cases, at the moment I think this is an acceptable solution. 
Unless there will be no better solution ;-)

> Also for the sake of completeness, not all objects can be cloned 1:1 so that
> the they are 100% independent and disconnected. Simple data container
> objects should be fine, though.

>> However, when I run it in PhantomJS 2.1.1 (Mac OS X) then it throws exception:
>>
>> "TypeError: Requested keys of a value that is not an object. in object.js
>> (line 9)"
>>
>> While I understand that "source" is passed as a non-object then I can't find
>> out what's causing it. At least debugging PhantomJS is a bit hard.
>
> Sorry, I don't have enough experience with PhantomJS to help with that. I
> suggested it for my current project, but was rejected. Their mailing list

Interesting, but I do not see more reliable way of executing tests in 
browser environment. I mean, you can use browser itself and execute 
manually, but that's not the point. I know also that there are some fake 
DOM solution for NodeJS, but I have no experience with that. Anyway, 
it's an off-topic subject :-)

> may be worth a try: https://groups.google.com/forum/#!forum/phantomjs

Thanks. I've handled the problem.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/
https://www.aslint.org/ - Accessibility validation tool

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Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 08:36 +0200
  Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 10:14 +0200
    Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 10:59 +0200
      Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 12:36 +0200
        Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 18:47 +0200
          Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 18:18 +0200
    Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 18:14 +0200
      Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-05 19:37 +0200
        Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 20:11 +0200
          Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 15:26 +0200
            Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-06 16:43 +0200
              Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 20:23 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-06 22:21 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 23:19 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-07 02:40 +0200
            Re: Object.defineProperties Stefan Weiss <krewecherl@gmail.com> - 2017-05-06 22:37 +0200
              Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 23:05 +0200
                Re: Object.defineProperties Stefan Weiss <krewecherl@gmail.com> - 2017-05-07 00:29 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-07 10:06 +0200
                Re: Object.defineProperties Stefan Weiss <krewecherl@gmail.com> - 2017-05-08 00:50 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-08 13:17 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-07 02:37 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-07 09:42 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-07 17:11 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-07 20:08 +0200
        Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 20:59 +0200
          Re: Object.defineProperties John G Harris <niam@jghnorth.org.uk.invalid> - 2017-05-06 10:35 +0100
  Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-05 08:32 +0200
  Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 18:24 +0200

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