The role of the datatype of the ajax method in jquery

I encountered a small problem today while maintaining a project. But I think this question is very helpful for the project. Write it down to help everyone. First let's look at a piece of code

$(".search").click(function(){
		$.ajax({
			type:"get",
		        url:"/communitys/CommunityShowController?method=listByAllCondition",
			dataType:"json",
			contentType: "application/x-www-form-urlencoded; charset=utf-8",
			data:
			{
				school: school,
				grade: grade,
				type: type
				
			},
			success: function(data){
				var showId = data[0].communityShowId;
				if(showId == 0){
 
					
					$("#list").html("No corresponding society");
					
				}else{
					$("#list").html('');
					var list = '';
					var data1 = data;
					
					$.each(data1, function (index, item) {  
	 					//loop to get data
						list += "<li><a href='/communitys/CommunityShowController?method=toEnter&communityShowId="+ item.communityShowId +"'><div class='img-box'><img src='/communitys/backpages/image/"+item.logo+"'></div><p class='img-cap'>"+item.name+"</p></a></li>";
						
					});
					$(list).appendTo("#list");
				}
            }
		});
	});

 This is a piece of code I'm learning and maintaining. The meaning is that when I click search, when there is content corresponding to the request, I will display a picture, and when there is no content, I will display a sentence " No corresponding community ".

This is already working code, the difference from my previous code is that I didn't set the datatype

Second

if(showId == 0){
//I wrote this statement as
if(data == '[{"communityShowId":"0","logo":"",name:""}]'){

 My original intention was to let data parse this json data directly, but since I didn't set the datatype, the array made of this json was parsed into a string. In this way, the statement below the if cannot be executed at all.

And when I set the datatype, ajax parses this string into json data format that matches my content. Second I set

var showId = data[0].communityShowId;

 This is equivalent to my parsing showId is to parse the json data of data, and I regard the json data of data as an array, each key will correspond to a key value, and I get showId as the first key in this json . When showId==0, that is, when the key value is 0, the if statement will be returned!