esp8266/libraries/ESP8266WiFi/examples/WiFiClientEvents/WiFiClientEvents.ino

/*
 *  This sketch shows the WiFi event usage
 *
 */

#include <ESP8266WiFi.h>

const char* ssid     = "your-ssid";
const char* password = "your-password";


void WiFiEvent(WiFiEvent_t event) {
    Serial.printf("[WiFi-event] event: %d\n", event);

    switch(event) {
        case WIFI_EVENT_STAMODE_GOT_IP:
            Serial.println("WiFi connected");
            Serial.println("IP address: ");
            Serial.println(WiFi.localIP());
            break;
        case WIFI_EVENT_STAMODE_DISCONNECTED:
            Serial.println("WiFi lost connection");
            break;
    }
}

void setup() {
    Serial.begin(115200);

    // delete old config
    WiFi.disconnect(true);

    delay(1000);

    WiFi.onEvent(WiFiEvent);

    WiFi.begin(ssid, password);

    Serial.println();
    Serial.println();
    Serial.println("Wait for WiFi... ");
}


void loop() {
    delay(1000);
}