React-Query generally returns some query states such as isLoading, isError. The library guarantees that these booleans are stable. This means we can be sure that the data is present if e. g. check for the onSuccess boolean. However, this - of course - isn't enough for the TS compiler. Even after the check, it assumes that the data can be undefined. What's the best way to let the TS compiler know that the data is present?
Here's an example from the docs:
function Todos() {
const { isLoading, isError, data, error } = useQuery('todos', fetchTodoList)
if (isLoading) {
return <span>Loading...</span>
}
if (isError) {
return <span>Error: {error.message}</span>
}
// --> The data is now sure to exist
return (
<ul>
{data.map(todo => ( // --> this will not work with the TS compiler.
<li key={todo.id}>{todo.title}</li>
))}
</ul>
)
}
react-query added discriminated unions in v3, so this generally works. You can discriminate by the status field as well as the derived boolean flags. However, there are two things that you need to keep in mind:
discriminated unions do not work if you destruct. This has nothing to do with react-query, but with TypeScript. If you take a field "out" of an object with destructuring, it can no longer discriminate that object.
react-query has an additional state: isIdle (or status === 'idle'), which will be true if the query is disabled via enabled: false.
Keeping these two things in mind, this should work:
function Todos() {
const queryInfo = useQuery('todos', fetchTodoList)
if (queryInfo.isLoading || queryInfo.isIdle) {
return <span>Loading...</span>
}
if (queryInfo.isError) {
return <span>Error: {error.message}</span>
}
// --> The data is now sure to exist
return (
<ul>
{queryInfo.data.map(todo => ( // --> TS is happy now
<li key={todo.id}>{todo.title}</li>
))}
</ul>
)
}
of course, you can also just check for isSuccess or status === 'success' to narrow the type.
When you need to load data once e.g. on the application start, I personally like to use "Gate" component. The role of the gate is to stop futher rendering as long as data is not loaded yet. When data is finally loaded I use context&customHook to read my initial data. At this point Im sure that my data will not be undefined. You can check a PoC here
Related
I have set code this way
errorGroup: any = FormGroup;
this.errorGroup = this.formBuilder.group({
errors: this.formBuilder.array([])
});
For repeat/add new data in group I have add this function which works fine.
addErrorGroup() {
return this.formBuilder.group({
error_code: ['',[Validators.required ]]
})
}
Get controls by this way. I think hear I'm missing something.
get f() { return this.errorGroup.controls.errors; }
In HTML
<select formControlName="error_code" name="error_code" (change)="errorCodeChange($event.target.value , i)">
<option *ngFor="..." value={{...}}>{{...}}</option>
</select>
<span *ngIf="f.error_code.errors.required" class="error-msg">This is required field.</span>
I got this error.
ERROR TypeError: Cannot read property 'errors' of undefined
If that error is coming from HTML, it's because your *ngIf condition is trying to read a value from an undefined object.
At the point where the view is rendered, and checked, it's entirely possible that f (incidentally, you should change that variable name to something more descriptive, but 🤷🏻♂️) doesn't have any errors populated yet, so will be undefined.
You can do one of two things here, either, you can wrap the whole thing in another *ngIf to ensure the error_code part of f is populate before accessing it:
<span *ngIf="f && f.error_code">
<span *ngIf="f.error_code.errors.required" class="error-msg">This is required field.</span>
</span>
Or, you can use the safe navigation operator:
<span *ngIf="f?.error_code?.errors?.required" class="error-msg">This is required field.</span>
Note the ? after each object key. This bails out when it hits the first null value, but, the app continues to work as it fails gracefully.
You can read more about it here: https://angular.io/guide/template-syntax#the-safe-navigation-operator----and-null-property-paths
How about if you just do below?
<span *ngIf="errorGroup.get('error_code').errors.required" class="error-msg">
This is required field.
</span>
so by doing this way, you don't need the f() getter in your component file.
I am a complete beginner in Software Development, and got introduced to a project which I have a hard time understanding and knowing where to start
this.isConfirmationCar = ko.computed(() => {
if (this.selectedTemplate() && this.selectedTemplate().Id ===
<number>Enums.PolicyEmailTemplates.ConfirmationOfCoverCar) {
return true;
} else {
return false;
}
});
It looks to be returning a boolean value and storing it within this.isConfirmationCar.
This being either true/false dependant on the argument defined as -
{ if (this.selectedTemplate() && this.selectedTemplate().Id === Enums.PolicyEmailTemplates.ConfirmationOfCoverCar) { return true; } else { return false; }
FYI - Knockoutjs has a great website with an excellent tutorial http://learn.knockoutjs.com/#/?tutorial=intro
It covers the ko.computed function in the intro worth a look!
What you have there is a computed observable which is nothing more but a function which inside of its body tracks ANY other observable used. Not only it tracks it but it would execute itself again and again on those tracked observables values mutating.
Computed observables are extremely useful. Note that they have various "options" in terms of how to defined them and some interesting siblings like the pureComputed observables.
In this example the computed isConfirmationCar is used to track the values of the other observables selectedTemplate and selectedTemplate. The moment any of those change that computed with refresh its value which is why it is used in this context for tracking isConfirmationCar.
Hope this helps.
I'm having the following error when trying to access a collection helper from a collection:
TypeError: Cannot read property 'username' of undefined
My helper in /imports/api/.../TaskUser.js :
TaskUser.helpers({
username() {
Meteor.subscribe('users');
elUser = Meteor.users.findOne({_id:this.userId})
return (elUser.username)
}});
My component
renderResponsables(){
return this.props.TaskUsers.map((OneTaskUser) => (
<tr key= {resp._id} onClick={() => this.insert(OneTaskUser._id)}>
<td>{OneTaskUser.username()}</td>
</tr>
));
}
It look like sync problem... but how can I know when it's sync in the client? I usually use subscription.ready() but here with a helper I do not know how to do it.
Advice1:
First add below package
meteor add msavin:mongol
then run the program and press "ctrl+m" it will show you the database tables and your subscribed data.there you can whether that your data has been subscribed or not.
Advice:2
Place your subscribe inside the autorun in oncreated
Template.Dashboard.onCreated(function(){
var self = this;
self.subscribe('users');
});
if above dosn't work then I need to check your users table how you created that and how you retrieve data from there correctly
Did you check this https://guide.meteor.com/react.html#data. You should use react-meteor-data package which provides a function called withTracker. Your subscription should go into it and you have to wrap your component with a container to pass the data.
Determine if NgForm Looks Exactly As It Did Before Any User-Input
It seems that form.dirty doesn't redact its value after it has been changed, and form.touched seems to always be false no matter what: dirty is touched, and touched is tetched.
template.html
<form #form="ngForm" (ngSubmit)="handleSubmission($event, {}, form)">
...
<input
#input
type="text"
[name]="item.title"
[(ngModel)]="item.estimate"
(ngModelChange)="handleEstimateChange(item, item.estimate, input, form)"
/>
...
</form>
component.ts
export class LeComponent {
#Input('data') public data: any;
public handleEstimateChange: Function;
constructor(private $: Sandbox) {
this.handleEstimateChange = $.debounce(this.handleEstimate.bind(this), (1000*0.2));
}
handleEstimate(item: any, estimate: number, input: HTMLInputElement, form: NgForm) {
if (!estimate) delete item.esitmate;
(this, item, estimate, input, form);
// Why does form.dirty never change back to pristine again???
}
}
In the TypeScript, I'm debouncing the ngModelChange handler to give Angular a chance to change the form.dirty value before I check it. This is because ngModelChange gets triggered before the NgForm object has been modified.
If !estimate, because estimate === "", then set it back to its original value of undefined. In this case, the form should look exactly like it did before any user-input had occurred.
However, when I put a breakpoint on the line right above the comment and I output form.dirty to the console, the NgForm never changes dirty back to false.
Is it possible to determine if the form looks exactly like it did before any user-input?
Obviously, I can write my own dirty logic, but wouldn't that mean that NgForm is kind of useless? There's got to be something I'm missing, right? How could dirty not mean dirty?
I've taken a look at some other SO questions -- the first one being similar but definitely not the question I am asking. They are asking if this is intentional -- I don't care; I'd like to know how to accomplish the goal above.
Close, but no cigar:
angular2 formcontrol stays dirty even if set to original value
Block routing if form is dirty [ Angular 2 ]
Angular 2 getting only the dirty values in a controlgroup
How do I programmatically set an Angular 2 form control to dirty?
Angular 2.x/4.x & bootstrap: patchValue does not alter dirty flag. Possible bug?
With template-driven forms and a very flat data model, I implemented it like this:
private currentProduct: IProduct;
private originalProduct: IProduct;
get isDirty(): boolean {
return JSON.stringify(this.originalProduct) !== JSON.stringify(this.currentProduct);
}
get product(): IProduct {
return this.currentProduct;
}
set product(value: IProduct) {
this.currentProduct = value;
// Clone the object to retain a copy
this.originalProduct = Object.assign({}, value);
}
But this only works for very simple cases.
As I mentioned in the comments, using reactive forms gives you more flexibility in managing your data model separate from your user entries.
What Was Most Useful
template.html
<form #form="ngForm" (ngSubmit)="handleSubmission($event, {}, form)">
...
<input
#input
type="text"
[name]="item.title"
[attr.name]="item.title"
[(ngModel)]="item.estimate"
(ngModelChange)="handleEstimateChange(item, item.estimate, input, form)"
/>
...
</form>
component.ts
export class LeComponent {
#Input('data') public section: any;
public handleEstimateChange: Function;
private resetFormControl = (input: HTMLInputElement, form: NgForm) => {
var name = input.name, control = form.controls[name];
control.reset();
// control.markAsPristine();
// control.setValue(undefined);
// control.updateValueAndValidity();
};
constructor(private $: Sandbox) {
this.handleEstimateChange = $.debounce(this.handleEstimate.bind(this), (1000*0.2));
}
handleEstimate(item: any, estimate: number, input: HTMLInputElement, form: NgForm) {
if (!estimate) this.resetFormControl(input, form);
(this, item, estimate, input, form);
// Why does form.dirty never change back to pristine again???
}
}
Note
[attr.name]="..." (template.html)
resetFormControl
Basically, simply deleteing the value was not enough because it was still present on the FormControl object (form.controls). To clear it properly, invoke control.reset() for the individual control -- this in-turn invokes .markAsPristine() which communicates to the parent NgForm. Also, input.name was empty as it was only represented by ng-reflect-name unless [attr.name] elucidated the same value -- [name] is really just there because its required by Angular.
Now, anytime an <input /> value changes -- and its falsey -- we reset the input ensuring that if all are falsey, Angular will automatically handle the NgForm's dirty-state correctly.
I have an array of Person objects
var persons = [
{Name:'John',Eligible:true},
{Name:'Mark',Eligible:true},
{Name:'Sam',Eligible:false},
{Name:'Edward',Eligible:false},
{Name:'Michael',Eligible:true}
];
and i am using select with ng-options like this:
<select ng-model="Blah" ng-options="person.Name for person in persons"></select>
I want to show the record with Eligible:false in red color.
So the problem is how do i use the ng-class in select inorder to achieve this? Since we are not using any option tag it wont work if i simply add ng-class in the select element itself.
You could create a directive that processed the options after the ngOptions directive is processed that updated them with the appropriate classes.
Update: The old code had a few bugs, and I've learned a bit since I answered this question. Here is a Plunk that was redone in 1.2.2 (but should work in 1.0.X as well)
Here is updated (Nov 30 '13 at 3:17) the Code:
app.directive('optionsClass', function ($parse) {
return {
require: 'select',
link: function(scope, elem, attrs, ngSelect) {
// get the source for the items array that populates the select.
var optionsSourceStr = attrs.ngOptions.split(' ').pop(),
// use $parse to get a function from the options-class attribute
// that you can use to evaluate later.
getOptionsClass = $parse(attrs.optionsClass);
scope.$watch(optionsSourceStr, function(items) {
// when the options source changes loop through its items.
angular.forEach(items, function(item, index) {
// evaluate against the item to get a mapping object for
// for your classes.
var classes = getOptionsClass(item),
// also get the option you're going to need. This can be found
// by looking for the option with the appropriate index in the
// value attribute.
option = elem.find('option[value=' + index + ']');
// now loop through the key/value pairs in the mapping object
// and apply the classes that evaluated to be truthy.
angular.forEach(classes, function(add, className) {
if(add) {
angular.element(option).addClass(className);
}
});
});
});
}
};
});
Here's how you'd use it in your markup:
<select ng-model="foo" ng-options="x.name for x in items"
options-class="{ 'is-eligible' : eligible, 'not-eligible': !eligible }">
</select>
It works like ng-class does, with the exception that it's on a per-item-in-the-collection basis.
In this scenario you can only apply ng-class only if you use ng-repeat with option tags:
<select ng-model="Blah">
<option ng-repeat="person in persons" ng-class="{red: person.Eligible}">
{{person.Name}}
</option>
</select>
This will give custom class to your 'Eligible' persons, but CSS won't work consistently across bowsers.
Plunker.
I wanted to comment on the accepted answer, but because I don't have enough reputation points, I must add an answer.
I know that this is an old question, but comments where recently added to the accepted answer.
For angularjs 1.4.x the proposed directive must be adapted to get it working again.
Because of the breaking change in ngOptions, the value of the option isn't anymore the index, so the line
option = elem.find('option[value=' + index + ']');
won't work anymore.
If you change the code in the plunker to
<select ng-model="foo" ng-options="x.id as x.name for x in items"
options-class="{ 'is-eligible' : eligible, 'not-eligible': !eligible }">
</select>
As result the value of the option tag will now be
value="number:x" (x is the id of the item object)
Change the directive to
option = elem.find('option[value=\'number:' + item.id + '\']');
to get it working again.
Of course this isn't a generic solution, because what if you have not an id in your object?
Then you will find value="object:y" in your option tag where y is a number generated by angularjs, but with this y you can't map to your items.
Hopes this helps some people to get their code again working after the update of angularjs to 1.4.x
I tried also to use the track by in ng-options, but didn't get it to work.
Maybe people with more experience in angularjs then me (= my first project in angularjs)?
The directive is one way, but I used a custom filter.
If you know how to select your element, you should be fine here. The challenge was to find the current option element inside the select. I could have used the "contains" selector but the text in the options may not be unique for items. To find the option by value, I injected the scope and the item itself.
<select ng-model="foo" ng-options="item.name|addClass:{eligible:item.eligible,className:'eligible',scope:this,item:item} for item in items"></select>
and in the js:
var app = angular.module('test', []);
app.filter('addClass', function() {
return function(text, opt) {
var i;
$.each(opt.scope.items,function(index,item) {
if (item.id === opt.item.id) {
i = index;
return false;
}
});
var elem = angular.element("select > option[value='" + i + "']");
var classTail = opt.className;
if (opt.eligible) {
elem.addClass('is-' + classTail);
elem.removeClass('not-' + classTail);
} else {
elem.addClass('not-' + classTail);
elem.removeClass('is-' + classTail);
}
return text;
}
})
app.controller('MainCtrl', function($scope) {
$scope.items = [
{ name: 'foo',id: 'x1',eligible: true},
{ name: 'bar',id: 'x2',eligible: false},
{ name: 'test',id: 'x3',eligible: true}
];
});
Here you can see it work.
The accepted answer did not work for me, so I found an alternative without a custom directive using track by :
<select ng-model="foo" ng-options="x.name for x in items track by x.eligible"></select>
Each option now gets the value x.eligible. In CSS you can style options with value = true (I think true has to be a string). CSS:
option[value="true"]{
color: red;
}
In case you not only want to show them in red color but prevent the user from selecting the options, you can use disable when:
<select
ng-model="Blah"
ng-options="person.Name disable when !person.Eligible for person in persons">
</select>
You can then use CSS to set the color of disabled options.
I can't write this as a comment, due to reputation, but I have updated the plunker for the accepted answer to work with Angular 1.4.8. Thanks to Ben Lesh for the original answer, it helped me a lot. The difference seems to be that newer Angular generates options like this:
<option class="is-eligible" label="foo" value="object:1">foo</option>
so the code
option = elem.find('option[value=' + index + ']');
wouldn't be able to find the option. My change parses ngOptions and determines what field of item was used for the label, and finds the option based on that instead of value. See:
http://plnkr.co/edit/MMZfuNZyouaNGulfJn41
I know I am a bit late to the party, but for people who want to solve this with pure CSS, without using a directive you can make a css class like this:
select.blueSelect option[value="false"]{
color:#01aac7;
}
This css rule says : Find all elements with value = false with tag name 'option' inside every 'select' that has a class "blueSelect" and make the text color #01aac7; (a shade of blue)
In your case your HTML will look like this:
<select class="form-control blueSelect" name="persons" id="persons1"
ng-options="person as person.name for person in $ctrl.persons track by person.Eligible"
ng-model="$ctrl.selectedPerson" required>
<option disabled selected value="">Default value</option>
</select>
The track by inside the ng-options is what will hold what to track the options by, or the "value" field of each option. Notice that depending on your project needs , you might have to do some tweaking to make this work as per your requirements.
But that's not going to work right when there's multiple options with the same value for the Eligible field. So to make this work, we create a compound expression to track by, that way we can have unique values to track by in each option. In this case we combine both fields Name and Eligible
So now our html will look like this
<select class="form-control blueSelect" name="persons" id="persons2"
ng-options="person as person.name for person in $ctrl.persons track by (person.name + person.Eligible)"
ng-model="$ctrl.selectedPerson" required>
<option disabled selected value="">Default value</option>
</select>
and our css :
select.blueSelect option[value*="False"]{
color:#01aac7;
}
Notice the * next to value, this is a regular expression which means to find the word "False" somewhere in the value field of the option element.
Quick Edit
You can also choose to disable the options with Eligible = False using the "disable when" in the ng-options expression , for example:
label disable when disable for value in array track by trackexpr
I'll leave how to use that in your case for you to find out ;-)
This works for simple css modifications, for more complex stuff you might need a directive or other methods. Tested in chrome.
I hope this helps someone out there. :-)
I've found another workaround that was easier than adding a directive or filter, which is to add a handler for the onfocus event that applies the style.
angular.element('select.styled').focus( function() {
angular.element(this).find('option').addClass('myStyle');
});