Tips for developing a personalized form validator for validating JSON data exclusively in Angular

Question

Tips for developing a personalized form validator for validating JSON data exclusively in Angular

Within my Angular application, there exists a reactive form that has a single control known as configJson, which is visually represented by a <textarea> element in the DOM.

The primary goal is to validate this specific form control to ensure that it only accepts valid JSON input from the user, triggering an error message if the input is invalid.

Shown below are the class and template for the component:

import { Component, OnInit } from '@angular/core';
import { FormControl, FormGroup } from '@angular/forms';

@Component({
  selector: 'app-configuration',
  templateUrl: './configuration.component.html',
  styleUrls: ['./configuration.component.scss']
})
export class ConfigurationComponent implements OnInit {

  form: FormGroup;

  constructor() {}

  ngOnInit() {
    this.form = new FormGroup({
      'configJson': new FormControl(),
    });

    // TODO: implement JSON validation
  }

  loadJsonConfiguration() {
    const config = JSON.parse(this.form.get('configJson').value);

    // additional logic here utilizing the parsed "config" object...
  }
}

<form [formGroup]="form">
  <div class="form-group">
    <label for="json-config-textarea">Parse from JSON:</label>
    <textarea
      class="form-control"
      id="json-config-textarea"
      rows="10"
      [formControlName]="'configJson'"
    ></textarea>
  </div>
  <div [hidden]="form.get('configJson').pristine || form.get('configJson').valid">
    Please insert a valid JSON.
  </div>
  <div class="form-group text-right">
    <button
      class="btn btn-primary"
      (click)="loadJsonConfiguration()"
      [disabled]="form.get('configJson').pristine || form.get('configJson').invalid"
    >Load JSON Configuration</button>
  </div>
</form>

json angular typescript angular-reactive-forms angular-validation

Answer 1

Answer №1

Initially, I attempted to modify the answer provided by the original poster (OP), but it was not approved by the peer reviewers for the following reason:

The proposed edit was meant to directly communicate with the post author and is not suitable as an edit. It would have been more appropriate as a comment or a separate answer.

Therefore, I have made adjustments and present my revised version:

import {AbstractControl, ValidationErrors, ValidatorFn} from '@angular/forms';

export function jsonValidator(control: AbstractControl): ValidationErrors | null {
  try {
    JSON.parse(control.value);
  } catch (e) {
    return { jsonInvalid: true };
  }

  return null;
};

import { Component, OnInit } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';

import { jsonValidator } from './json.validator';

@Component({
  selector: 'app-configuration',
  templateUrl: './configuration.component.html',
  styleUrls: ['./configuration.component.scss']
})
export class ConfigurationComponent implements OnInit {

  form: FormGroup;

  ngOnInit() {
    this.form = new FormGroup({
      configJson: new FormControl(Validators.compose(Validators.required, jsonValidator))
    });
  }

  loadJsonConfiguration() {
    ...
  }
}

Answer 2

Initially, I attempted to modify the answer provided by the original poster (OP), but it was not approved by the peer reviewers for the following reason:

The proposed edit was meant to directly communicate with the post author and is not suitable as an edit. It would have been more appropriate as a comment or a separate answer.

Therefore, I have made adjustments and present my revised version:

import {AbstractControl, ValidationErrors, ValidatorFn} from '@angular/forms';

export function jsonValidator(control: AbstractControl): ValidationErrors | null {
  try {
    JSON.parse(control.value);
  } catch (e) {
    return { jsonInvalid: true };
  }

  return null;
};

import { Component, OnInit } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';

import { jsonValidator } from './json.validator';

@Component({
  selector: 'app-configuration',
  templateUrl: './configuration.component.html',
  styleUrls: ['./configuration.component.scss']
})
export class ConfigurationComponent implements OnInit {

  form: FormGroup;

  ngOnInit() {
    this.form = new FormGroup({
      configJson: new FormControl(Validators.compose(Validators.required, jsonValidator))
    });
  }

  loadJsonConfiguration() {
    ...
  }
}

Answer 3

Answer №2

To ensure that only valid JSON is accepted in a form, one solution is to create a custom form validator and attach it to the form control. The validator will check if the input is valid JSON.

Here is an example of how the custom validator can be implemented:

import {AbstractControl, ValidationErrors, ValidatorFn} from '@angular/forms';

export function jsonValidator(): ValidatorFn {
  return (control: AbstractControl): ValidationErrors | null => {
    const error: ValidationErrors = { jsonInvalid: true };

    try {
      JSON.parse(control.value);
    } catch (e) {
      control.setErrors(error);
      return error;
    }

    control.setErrors(null);
    return null;
  };
}

Unit tests can be written to ensure the validator functions correctly:

import { FormControl, ValidationErrors, ValidatorFn } from '@angular/forms';
import Spy = jasmine.Spy;

import { jsonValidator } from './json.validator';

describe('JSON Validator', () => {
  // Test cases go here...
});

To apply the custom validator in the component, add it in the ngOnInit method:

    this.form.get('configJson').setValidators([
      Validators.required,
      jsonValidator(),
    ]);

With the custom validator in place, the component's class will look like this:

import { Component, OnInit } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';

import { jsonValidator } from './json.validator';

@Component({
  selector: 'app-configuration',
  templateUrl: './configuration.component.html',
  styleUrls: ['./configuration.component.scss']
})
export class ConfigurationComponent implements OnInit {

  form: FormGroup;

  constructor() {}

  ngOnInit() {
    // Form initialization and adding validators
  }

  loadJsonConfiguration() {
    // Logic to parse and use the JSON configuration
  }
}

Answer 4

To ensure that only valid JSON is accepted in a form, one solution is to create a custom form validator and attach it to the form control. The validator will check if the input is valid JSON.

Here is an example of how the custom validator can be implemented:

import {AbstractControl, ValidationErrors, ValidatorFn} from '@angular/forms';

export function jsonValidator(): ValidatorFn {
  return (control: AbstractControl): ValidationErrors | null => {
    const error: ValidationErrors = { jsonInvalid: true };

    try {
      JSON.parse(control.value);
    } catch (e) {
      control.setErrors(error);
      return error;
    }

    control.setErrors(null);
    return null;
  };
}

Unit tests can be written to ensure the validator functions correctly:

import { FormControl, ValidationErrors, ValidatorFn } from '@angular/forms';
import Spy = jasmine.Spy;

import { jsonValidator } from './json.validator';

describe('JSON Validator', () => {
  // Test cases go here...
});

To apply the custom validator in the component, add it in the ngOnInit method:

    this.form.get('configJson').setValidators([
      Validators.required,
      jsonValidator(),
    ]);

With the custom validator in place, the component's class will look like this:

import { Component, OnInit } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';

import { jsonValidator } from './json.validator';

@Component({
  selector: 'app-configuration',
  templateUrl: './configuration.component.html',
  styleUrls: ['./configuration.component.scss']
})
export class ConfigurationComponent implements OnInit {

  form: FormGroup;

  constructor() {}

  ngOnInit() {
    // Form initialization and adding validators
  }

  loadJsonConfiguration() {
    // Logic to parse and use the JSON configuration
  }
}

Tips for developing a personalized form validator for validating JSON data exclusively in Angular

Answer №1

Answer №2

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