How to detect current slide in swiper js?

Expanding on the answers that already refer to the realIndex property, here is a method for fetching the current slide's element by using realIndex as well as the slides property (an array containing all slides of the instance) to get the slide-element:

let index_currentSlide = instance_swiper.realIndex;
let currentSlide = instance_swiper.slides[index_currentSlide]

You can make use of this when constructing the instance by (for example) fetching the current slide whenever the slideChange event occurs and manipulating the element:

const instance_swiper = new Swiper(".swiper-container", {
  on: {
    slideChange: function () {
      const index_currentSlide = instance_swiper.realIndex;
      const currentSlide = instance_swiper.slides[index_currentSlide]
      //
      currentSlide.style.background = "red";
    },
  },
});

As of May 2016 they have added the realIndex property!

swiper.realIndex

https://github.com/nolimits4web/Swiper/pull/1697

Notice:

• property is returned as a string
• property starts with 0, unlike activeIndex in loop mode which in my case started with 1

its very easy. just use this:

swiper.activeIndex