Angular: What does "Cannot read property 'childNodes' of null" trying to tell?

Recently, I ran into the following error, it has no obvious problem at first until part of my component template didn't show a thing until a click event is triggered the at the screen.

Cannot read property 'childNodes' of null

The error do not directly indicate which component or code in a template has gone wrong, but you know it's an error about certain part of the code is referring to "childNodes" on a null object.

Finding out the root cause

To find out where in the template has gone wrong, I didn't suspect it's problem with HTML template. I had started with checking my component class code, and though some binding values weren't pass correctly into the template code (the template code look fine, not bad syntax at all!).

Until I gave up trying consciously, I blindly test by removing of the HTML code part by part. This is where it shed me the ray of hope, eventually, I found out it's ion-card Ionic's component doesn't accept [innerHtml] correctly.

If you insist on using ion-card, you need a proper "child node" place inside it (so now I learnt, "child node" means the child element of a parent node "ion-card".), for ion-card, one of the options is ion-card-content.

I changed my code from:

<ion-card [innerHtml]="content" padding></ion-card>

to

<ion-card>
  <ion-card-content [innerHtml]="content"></ion-card-content>
</ion-card>

Separating [innerHtml] from ion-card would solve the childNode problem above. You might have different parent node causing the null childNodes issue too. So to prevent further time wasting effort finding the root-cause and if you run into similar issue, just keep in mind, if you get similar error, it means there is problem in your template/html code.

TypeError: Found non-callable @@iterator - Migration of Angular 7 to 8 (upgrading Ionic: 4.6.0 > 4.7.1)

Troubleshoot migration problems

TypeError: Found non-callable @@iterator

TypeError: Found non-callable @@iterator

The non-descriptive error message Found non-callable @@iterator, for new Angular 8 user like me, has made the upgrading journey a difficult experience.

And my finding, the cause of the problem above is due to the way interceptor written in Angular 7.

Causes: HttpRequest's headers "set"

I noticed the use of request.headers.set() causing the issue above. My sample code (causes):

intercept(req: HttpRequest, next: HttpHandler): Observable> {
  let headers = req.headers;
  const sampleToken = 'SAMPLE_TOKEN';
  headers = req.headers.set('Authorization', sampleToken);

  return next.handle(req.clone({ headers }));
}

After multiple trial and error, the only way to resolve is avoid using the same way to add header with such solution.

Solution: Headers modification

- on one single header modification, do the following

const yourToken = 'YOUR_TOKEN';
const apiReq = req.clone({
  headers: new HttpHeaders({'Authorization', yourToken})
});
return next.handle(apiReq);

- on multiple headers modification, do the following

const headers = { Authorization: authToken };
const apiReq = req.clone({
  setHeaders: headers
});
return next.handle(apiReq);

P/S: header value must be in string value

Troubleshooting Cakephp 3 showing "Blank page" (Clue: internationalisation (i18n))

Understanding i18n

To implement multiple languages in your webpage, you need internationalisation (or i18n, start with an alphabet "i", 18 alphabet in the middle and end with an "n").

If you have came across this feature, you'll know you need your static content written in the following format:

echo __('Text to be translated');

And the "Text to be translated" will appear in your Locale folder's in "po" formatted file.

Potential cause of the "Blank page"

Overview of the findings, the "blank" page appears in:

• complete blank screen and show nothing, 
• browser is showing correct code in the HTML page source (without HTML code from chosen layout)
• page goes blank without any warning/error messages

Things to check for the issue

• is the "__()" written correctly? Make sure it's 2 underscores + text in the bracket.
• Search your source code and find if there is any mistakenly written single underscore "_()" i18n syntax
• be warned, you won't get any error message from single underscore i18n syntax "_()" mistake

References:
CakePHP 3 - Internationalization & Localization
CakePHP 3 - Global function __()

Troubleshooting Android Flashing Custom ROM / Recovery

Troubleshooting

Cannot boot into TWRP without rooting

The sentence above is somewhat misleading, "without rooting" doesn't mean "no flash", I said so because I was inexperienced, so I keep trying to boot without flashing. And I've stuck in the retrying loop until I gave up several for 2 weeks of countless attempts.
I would rather name the title to "Flashing TWRP without rooting" before anyone else get stuck in the hopeless loop again.

In order to boot into custom recovery, you cannot skip flashing the custom recovery first. Lesson learned,

No One Can Boot Into Twrp Without Flashing With TWRP Recovery first!

As a Asus device user, I did trial and error this many time until I finally learnt and come to a conclusion "we can't boot into custom recovery without flashing them beforehand".

Let me summarise the general steps after I've gone through wide amount of online articles:

1. adb reboot bootloader (boot into fastboot mode)
2. fastboot devices (to make sure your device is connected)
3. fastboot flash recovery twrp.img
4. fastboot reboot (or press and hold Volume button to boot into TWRP recovery mode)

What I've learned from this:

- Flashing TWRP will still unlock the bootloader in your device

- for Asus, flashing TWRP custom recovery will also root your device (void warranty)

I haven't seen any of my trial and error that won't root my device after flashing TWRP recovery.

You can check your device info by running command below:

  fastboot oem device-info

The Root status will show as "Rooted"

Endless re-booting bootloader/bootup screen

I encounter this problem after flashed an incorrect recovery into my device.

Potential cause: Usually, you'll run into this problem after running the command below in fashboot mode (with a unsuitable recovery file):

  fastboot flash recovery example-recovery-filename.img

Solution

To resolve this, you'll have to find the correct version of recovery rom that fits your device. If you spent hours looking for one and still no luck getting one, then you may need to consider a more generally owned by the developer community or learn to compile a custom recovery by yourself. TWRP itself is a open source project, if you need something not existence

For TWRP custom recovery, please visit: https://twrp.me/Devices/

For Asus, I usually have to keep googling at their dedicated Asus Forum - Zentalk for specific/older device's discussion.

For Asus device, if you run into unrecoverable flashing issue (bricked), you can always get back the stock (official) version of ROM/firmware from Asus official support website and flash your device back into the original device firmware.

* note: avoid losing all your data, always backup your device before flashing anything

Booting into Fastboot/Recovery Mode

1) How do I get into fastboot mode?
Run the command below in order to boot into fastboot mode from "normal UI" screen (the UI show up for normal daily use made for general user.):

  adb reboot fastboot

You can boot into fastboot mode by restart/power on your phone by holding Volume Up button (for Asus Android phone).
Steps:

1. From power off mode, press and hold volume buttons
1. volume up - for fastboot mode
2. volume down - for recovery mode
2. Keep on holding the volume button after device is powered on until the expected screen mode is correctly shown.

*note: Booting into fastboot/recovery mode doesn't render your warranty void.

2) "adb: command not found", what is missing?
Which command unavailable in your system, you can't proceed any further.
To install required tools, you need run the command above using:

• (Window) adb.exe (ROM flashing kits)
• (Unix) For Unix system, 2 choices: 
• Install full official android development tools Android Studio (follow their installation tutorials), or 
• Visit Android Studio (same url as above), scroll until Command Line Tools only section and install the only the command line tools, which will install required general tools like adb (Android Debug Bridge) and fastboot tools to access to your android devices through USB cable.

Some useful articles that worth your time (for understanding about flashing custom recovery):
Discover hidden fastboot commands
Guide to customise Android device
Install TWRP recovery on Android (no root)

Angular 7 + Ionic 4: No provider for NavController! (Clue: incorrect module name imported)

NullInjectorError: No provider for NavController!

After switching from AngularJs to Angular 7 and Ionic 4, I've came across a few new issues where led me to high dependence on StackOverflow.
For certain edge cases without a certified answer, as plus Ionic 4 is still in beta build (during my writing of this article). If SO don't has the answer, I'll have to spend more hours on the issue by diving into the error message and core library.

First thing came into my mind when I first look at the error message:

What is NavController has to do with my code while I've never imported it into any of my component. I didn't use NavController at all in my code as Ionic mentioned they are deprecated in Ionic4

After spent 2-3 days of clueless bug hunting, it's found how I imported IonicModule is the culprit!

Capital letter '@Ionic/angular' should be '@ionic/angular'

In short, the solution is to check your module name if they are written in correct case format (yes case sensitive, I've learned my painful lesson).

Quick Solution:
@Ionic/angular should be @ionic/angular

No provider for NavController

...
ERROR Error: StaticInjectorError(AppModule)[HrefDelegate -> NavController]: 
StaticInjectorError(Platform: core)[HrefDelegate -> NavController]: 
  NullInjectorError: No provider for NavController!
  at NullInjector.push../node_modules/@angular/core/fesm5/core.js.NullInjector.get (core.js:717)
  at resolveToken (core.js:954)
  at tryResolveToken (core.js:898)
  at StaticInjector.push../node_modules/@angular/core/fesm5/core.js.StaticInjector.get (core.js:795)
  at resolveToken (core.js:954)
  at tryResolveToken (core.js:898)
  at StaticInjector.push../node_modules/@angular/core/fesm5/core.js.StaticInjector.get (core.js:795)
  at resolveNgModuleDep (core.js:17656)
  at NgModuleRef_.push../node_modules/@angular/core/fesm5/core.js.NgModuleRef_.get (core.js:18345)
  at resolveDep (core.js:18716)
...

Like the error message above, Ionic4 didn't really provide very informative clue that helps debugger identify what is rootcause. So yeah, there are risks when we use beta library building our project...
I believe soon later, the error message would be clearer once it's near its official stable build release date.
There is also a slightly useful warning message obtained from browser console, posted as below

...
There are multiple modules with names that only differ in casing.
This can lead to unexpected behavior when compiling on a filesystem with other case-semantic.
Use equal casing. Compare these module identifiers:
// ... list of affected files ...
/node_modules/@ionic/angular/dist/providers/action-sheet-controller.js
/node_modules/@Ionic/angular/dist/util/overlay.js
/node_modules/@ionic/angular/dist/index.js
/node_modules/@Ionic/angular/dist/providers/action-sheet-controller.js
/node_modules/@Ionic/angular/dist/util/util.js
...

Well, the messages in debugger do shine some light about the ambiguous and conflicting module names, the list of affected files don't really tell what has gone wrong.
Hope this article could help some not-so-lucky guys out there who fell into traps set by ourselves.