Changing handle on Angular2 checkbox

I have a checkbox and I want to use (change)

on it. The default is "checked", but after clicking I want a clean text input "Activation Key". After re-checking, I want to create a guid and add to the input again. How to get if a checkbox is checked or not?

<div class="checkbox">
    <label>
       <input type="checkbox" checked (change)="handleChange($event)" > 
           Generate key
    </label>
</div>

      

        
        
        
      

    

TS

handleChange(e) {
    var isChecked = e.isChecked;
    if (isChecked) {
        this.gatewayForm.patchValue({ 'activationKey': this.guid() });
    }
    else {
       this.gatewayForm.controls['activationKey']
           .setValue('', { onlySelf: true });
    }
}