reactive form validation in angular 7 code example

Example 1: angular validators number only in reactive form

new FormControl({value: field.value}, [Validators.required, Validators.pattern(/^-?(0|[1-9]\d*)?$/)])

Example 2: custom validator

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

export function blue(): ValidatorFn {  
    return (control: AbstractControl): { [key: string]: any } | null =>  
        control.value?.toLowerCase() === 'blue' 
            ? null : {wrongColor: control.value};
}
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Example 3: ng2 validations angular using reactiveforms

<form [formGroup]="form">
  <input type="password" formControlName="password"/>
  <p *ngIf="form.controls.password.errors?.required">required error</p>
  <input type="password" formControlName="certainPassword"/>
  <p *ngIf="form.controls.certainPassword.errors?.equalTo">equalTo error</p>
</form>

Example 4: formgroup check if valid

form: FormGroup;

onSubmit(){
    //checks if form is valid
       if( this.form.valid){
          //more code here
        }
}