Angular checkbox control accessor returning its value instead of true/false

advanced-checkbox-control-value-accessor.directive.ts

import {Directive, ElementRef, Renderer2, forwardRef, Input} from '@angular/core';
import {ControlValueAccessor, NG_VALUE_ACCESSOR} from '@angular/forms';

export const CHECKBOX_VALUE_OVERRIDE_ACCESSOR: any = {
    provide: NG_VALUE_ACCESSOR,
    useExisting: forwardRef(() => AdvancedCheckboxControlValueAccessor),
    multi: true,
};

/**
 * The accessor for writing a value and listening to changes on a checkbox input element.
 * Writes `value` if checked and `offvalue` otherwise.
 *
 *  ### Example
 *  ```
 *  <input type="checkbox" name="rememberLogin" ngModel value="On" offvalue="Off">
 *  ```
 *
 *  ### Installation
 *  ```
 *  import {AdvancedCheckboxControlValueAccessor} from 'advanced-checkbox-control-value-accessor.directive';
 *  @NgModule({
 *      declarations: [
 *          AdvancedCheckboxControlValueAccessor
 *      ]
 *  })
 *  export class AppModule {
 *  }
 *  ```
 */
@Directive({
    selector: 'input[type=checkbox][formControlName],input[type=checkbox][formControl],input[type=checkbox][ngModel]',
    host: {'(change)': 'onChange()', '(blur)': 'onTouched()'},
    providers: [CHECKBOX_VALUE_OVERRIDE_ACCESSOR]
})
export class AdvancedCheckboxControlValueAccessor implements ControlValueAccessor {
    _state: boolean;
    _fn: Function;

    onChange = (_: any) => {};
    onTouched = () => {};

    @Input() value: any;
    @Input() offvalue: any = null;

    constructor(private _renderer: Renderer2, private _elementRef: ElementRef) {}

    writeValue(value: any): void {
        this._state = value === this.value;
        this._renderer.setProperty(this._elementRef.nativeElement, 'checked', this._state);
    }

    registerOnChange(fn: (_: any) => {}): void {
        this._fn = fn;
        this.onChange = () => {
            fn(this._elementRef.nativeElement.checked ? this.value : this.offvalue);
        };
    }

    registerOnTouched(fn: () => {}): void { this.onTouched = fn; }

    setDisabledState(isDisabled: boolean): void {
        this._renderer.setProperty(this._elementRef.nativeElement, 'disabled', isDisabled);
    }
}