Serial

isConnected()

// EXAMPLE USAGE
void setup()
{
  Serial.begin();   // open serial over USB
  while(!Serial.isConnected()) // wait for Host to open serial port
    Particle.process();

  Serial.println("Hello there!");
}

Another technique is to use waitFor which makes it easy to time-limit the waiting period.

// EXAMPLE USAGE
void setup()
{
  Serial.begin();   // open serial over USB

  // Wait for a USB serial connection for up to 30 seconds
  waitFor(Serial.isConnected, 30000);

  Serial.println("Hello there!");
}

Since 0.5.3 Available on Serial.

Since 0.6.0 Available on Serial and USBSerial1.

Used to check if host has serial port (virtual COM port) open.

Returns:

• true when Host has virtual COM port open.