startDeviceScan() Method to scan the available BLE devices and setTimeout() function to stop the scanning after 2seconds by using stopDeviceScan() Method.

ScanBleDevices.js

  //SCANNING BLUETOOTH DEVICES
  function scanAvailableBleDevice() {

    let devicesObj = {};
     
     // _BleManager is the BleManager instance, We already import and initialize the instance in _BleManager variable
     // If you need any clarification please check the "Usage" section, we already discussed above in this blog.
    _BleManager.startDeviceScan( 
      [null],
      { allowDuplicates: false },
      (error, device) => {
        if (error) {
          let errorCode = JSON.stringify(error.errorCode);
          let errorMessage = JSON.stringify(error.reason);
          if (errorCode == "600") {
            if (errorMessage.startsWith(`"Undocumented scan`)) {
              alert("Too Many attempts to scan,please try again later");
            } else {
              console.log(errorMessage)
              alert("Something went wrong in scanning devices")
            }
          }
        } else {
          console.log(device)
          // Store the device object in the "deviceObj" variable of key-value pair, Key is device ID, Value is entire device object
          // Because of due to the scanning time period(I used 2seconds for scanning devices by using setTimeout()) it scan the same device repeatedly over the time period,
          // So store Key-value pair to remove the duplicate device by using device ID after completed the scanning time period
          devicesObj[device.id] = device; 
        }
      }
    );

    //stop scanning device after 2seconds
    setTimeout(() => {
      let devices = [];
      _BleManager.stopDeviceScan();
      let deviceIds = Object.keys(devicesObj);
      if (deviceIds.length) {
        let noDuplicateDevices = new Set(deviceIds);
        noDuplicateDevices.forEach((deviceId) => {
          devices.push(devicesObj[deviceId]);
        });
        console.log(devices) // After remove the duplicate devices, Duplicate devices means same device is stored repeatedly in the scanning
      }
      else {
        alert("No available BLE devices") //After stops the scanning no available devices
      }
    }, 2000);
  }