How to display the dropdown values based on other dropdown selected value using typescript in Angular 4

Question

I want to change dropdown value based on selected other dropdown selected. this is HTML

 <select class="form-control" name="category_id" formControlName="category_id" (change)="changeProfession($event.target.value)">
                                    <!-- <option value="" d>Select Category (required)</option> -->
                                    <option *ngFor='let surveyCategory of surveyCategoryList' [ngValue]="surveyCategory._id">{{ surveyCategory.category }}</option>
                                    <app-field-error-display [displayError]="this.validationService.isFieldValid(updateProfileForm,'category_id')">
                                    </app-field-error-display>
                               </select>

here I want to get value as per the selected category

<div class="form-group label-floating select_lang">
                                <label class="control-label">Profession</label>
                                <select class="form-control" name="profession_id" formControlName="profession_id" >
                                     <!-- <option value="" >Select Category (required)</option> -->
                                    <option *ngFor='let profession of ProfessionList' [ngValue]="profession._id">{{ profession.profession }}</option>
                                    <app-field-error-display [displayError]="this.validationService.isFieldValid(updateProfileForm,'profession_id')">
                                    </app-field-error-display>
                               </select>

                            </div>

this is the ts file

changeProfession(categoryid){
    debugger;
    this.authService.getProfessionList(categoryid).subscribe(data => {
        debugger;
        if (data.success) {
            debugger;
            this.ProfessionList = data.profession;
            console.log(data);
            setTimeout(() => {
            //if (obj.survey_category_id)
                    //this.updateProfileForm.controls['profession_id'].setValue(obj.profession_id._id);
                 $('.select_lang').removeClass('is-empty');
            }, 10);
        }

    });
}

and this is the service file

// Get survey profession list
 getProfessionList = function (categoryid) {
     debugger;
    return this.http.get(this.api_url + 'profession/list/'+ categoryid, this.getAuthHeaderOption()).map(res => res.json());
}

When I am calling this event then category id is passing but value in not showing. Please tell me what I am doing wrong here .

Answer 1

The Angular way of implementing your requirement will be slight different than the way you have done.

in your component.ts file add below code where you have initialize the form :

 this.sampleForm.controls['category_id'].valueChanges.subscribe((value) => {
       this.authService.getProfessionList(value).subscribe(data => {
            this.ProfessionList = data.profession;
       }); 
 });  

replace sampleForm with your formGroup Name. Also note that the value of data.profession should be array of objects.

Here is sample working Stackblitz link : Working Demo