Error encountered in Angular8 Template Driven Form: TypeError - Attempt to access property 'ProviderName' of undefined resulting in Object.eval throwing an error in updateDirectives

An error has occurred with the template causing an issue.

    ProviderComponent.html:4 ERROR TypeError: Cannot read property 'ProviderName' of undefined
    at Object.eval [as updateDirectives] (ProviderComponent.html:4)
    at...
provider.component.html
    <div class="form-row">
        <div class="form-group col-6">
            <input class="form-control" name="ProviderName"  #ProviderName="ngModel" 
          [(ngModel)]="providerService.selectedProvider.ProviderName" placeholder="Provider Name" 
           required>
        </div>
        ...

app.module.ts

    import { BrowserModule } from '@angular/platform-browser';
    import { NgModule } from '@angular/core';
    
    ...

proivder.service.ts:

    import { Injectable } from '@angular/core';
    
    ...

provider.component.ts:

    import { Component, OnInit } from '@angular/core';
    import { ProviderService } from '../shared/provider.service'; 
    
    ...

Answer №1

It is important to include the ‘?’ in the template because there are instances where selectedProvider is undefined.

To avoid a null exception, use providerService.selectedProvider?.ProviderName.

Angular attempts to resolve this property during binding validation in change detection, but encounters an issue with null values. The '?' operator serves as a null safety operator.

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