How do you declare multiple characteristics in Web Bluetooth?

I have no clue how to implement multiple characteristics:

Currently my code works perfectly when a single characteristic is declared/implemented:

   .then((service) => {     pushlog("Getting Shutdown Characteristic...");     shdn = service.getCharacteristic(       "33ca7a02-c95f-4bca-a8bb-6692930216d0"     ); return shdn; 

However, when I attempt to implement multiple characteristics next.js error (the plain-text uuid's work with web bluetooth):

.then((service) => {     pushlog("Getting Characteristic...");     heart_rate_measurement = service.getCharacteristic(       "heart_rate_measurement"     );     temperature_measurement = service.getCharacteristic(       "temperature_measurement"     );     shdn = service.getCharacteristic(       "33ca7a02-c95f-4bca-a8bb-6692930216d0"     );     stim = service.getCharacteristic(       "b71ce29e-7353-40bf-a4dd-b0c03593e0ba"     );     battery = service.getCharacteristic("battery_level");      return (       shdn, heart_rate_measurement, temperature_measurement, stim, battery     );   }) 

My read/write code doesn't work -

.then((shdn) => {     pushlog("Writing to Shutdown Characteristic...");      // Writing 1 is the signal to reset energy expended.     let resetEnergyExpended = Uint8Array.of(0x01);     return shdn.writeValue(resetEnergyExpended);   }) 

Am I declaring these additional characteristics incorrectly? All the resources next.js error I see are for android BLE and not web bluetooth. I saw some solutions using classes, however, I'm using next.js and I'm clueless of how to implement vanilla JS classes into react.

Answers 1: of How do you declare multiple characteristics in Web Bluetooth?

.then((service) => {     pushlog("Getting Characteristic...");     heart_rate_measurement = service.getCharacteristic(       "heart_rate_measurement"     );     temperature_measurement = service.getCharacteristic(       "temperature_measurement"     );     shdn = service.getCharacteristic(       "33ca7a02-c95f-4bca-a8bb-6692930216d0"     );     stim = service.getCharacteristic(       "b71ce29e-7353-40bf-a4dd-b0c03593e0ba"     );     battery = service.getCharacteristic("battery_level");      return Promise.all([       shdn, heart_rate_measurement, temperature_measurement, stim, battery     ]);   }) .then(([shdn, heart_rate_measurement, temperature_measurement, stim, battery]) => {     pushlog("Writing to Shutdown Characteristic...");      // Writing 1 is the signal to reset energy expended.     let resetEnergyExpended = Uint8Array.of(0x01);     return shdn.writeValue(resetEnergyExpended);   })