Hola, estoy tratando de obtener una subcadena de una cadena basada en algunos cálculos, pero aparece este error en la consola del navegador:

 TypeError: Cannot read properties of undefined (reading 'substring') at MessageVariantCardInputComponent.onInput at MessageVariantCardInputComponent_input_HostBindingHandler

cuando se usa el ejemplo de código a continuación para obtener el valor de subcadena de "valor"

Código:

 @HostListener('input') onInput() { this.triggerFound = false; this.triggerName = ''; const native = this.element.nativeElement; console.log("=== native dropdown", native) const value = native.value; const currentPos = native.selectionStart - 1; for (const key of Object.keys(this.triggers)) { const trigger = this.triggers[key]; const triggerLen = trigger.length; const extractedString = value.substr(currentPos - triggerLen + 1, triggerLen); const found = extractedString === trigger; const isFirstTrigger = key === 'firstElement'; if ((isFirstTrigger && found && currentPos === 0) || // allow first element trigger only when current pos is 0 (!isFirstTrigger && found) ) { this.triggerFound = true; this.triggerName = trigger; break; } } }