How to place the Slick slider initialization script in an external file?

When I put the Slick slider initialization script in an external JS file, the slider stops working.

$(document).ready(function(){ $('.slider-for').slick({ infinite: true, slidesToShow: 1, slidesToScroll: 1, initialSlide: 0, arrows: false, fade: true, speed: 300, // fade: true, asNavFor: '.slider-nav' }); $('.slider-nav').slick({ slidesToShow: 3, slidesToScroll: 1, asNavFor: '.slider-for', dots: false, centerMode: true, focusOnSelect: true }); });