This snippet is allowing to trigger some functions when browser window size changes (you know, like CSS media queries, changes only when it passes through milestone)

sizeChange.js

// Created by Valeriy Sagatovskiy

// Create the new instance of changeWithSize with parameters :
// - unit: milestone in pixels causing callbacks, f.e. "1024"
// - dimension: which dimension is watched for changes - "width" or "height"
// - b_callback: will be called if dimension changes from big to small
// - a_callback: will be called if dimension changes from small to big

// If you pass only one callback, it will be called in both directions
// If you don't want any actions on the certain direction, just pass 'null' instead of callback

var changeWithSize = function(unit, dimension, b_callback, a_callback) {
	var trigger = undefined;
	var size = undefined;
	unit = parseFloat(unit);
	if (a_callback === undefined) {
		a_callback = b_callback;
	}
    if (a_callback === null) {
        a_callback = function() {};
    }
    if (b_callback === null) {
        b_callback = function() {};
    }
	checkDimension();
	if (size() >= unit) {
		trigger = true; // за точкой изменения
	} else trigger = false; // перед точкой изменения

	window.addEventListener('resize', function() {
		var _size = size();
		if (_size >= unit) {
			if (trigger !== true) {
				a_callback();
				trigger = true;
			}
		}
		if (_size < unit) {
			if (trigger !== false) {
				b_callback();
				trigger = false;
			}
		}
	})
	function checkDimension() {
		if (dimension !== undefined && dimension !== null && dimension !== "") {
			if (dimension === "width") {
				return size = function() {
					return document.body.clientWidth;
				};
			}
			if (dimension === "height") {
				return size = function() {
					return document.body.clientHeight;
				}
			} else return console.error("ChangeWithSize: no dimension parameter!");
		} else return console.error("ChangeWithSize: no dimension parameter!");
	}
}

// license - MIT