Google Earth engine app - maximum image synthesis analysis using S2 image

First of all, let's not make low-level mistakes , Let's go and have a look at gee Official document https://developers.google.com/earth-engine/tutorials/tutorial_js_03

Here we are using this program , Sometimes addition and subtraction is used add perhaps subtract etc. , Instead of directly using the symbols of addition, subtraction, multiplication and division that match ”+“,”-“,”*“,”/“ These symbols , because GEE The client used in it runs ,

In this article, we use a about image every 15 The process of screening once a day , That is to search every half a month

Code ：

var geometry = 
    /* color: #d63000 */
    /* displayProperties: [
      {
        "type": "rectangle"
      }
    ] */
    ee.Geometry.Polygon(
        [[[-115.06328125, 40.534424706292405],
          [-115.06328125, 38.98050493805514],
          [-112.95390625, 38.98050493805514],
          [-112.95390625, 40.534424706292405]]], null, false);

var startDate = '2019-01-01';  
var endDate = '2022-01-01';

var aoi &