jQuery.getJSON でファイルがないのを明示する方法です。
.fail がポイントです。
html ファイル
index.html
<!DOCTYPE html>
<html lang="ja">
<head>
<meta http-equiv="Pragma" content="no-cache" />
<meta http-equiv="Cache-Control" content="no-cache" />
<meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8" />
<script src="/js/jquery-3.3.1.min.js"></script>
<script src="example_json.js"></script>
<title>example_json</title>
</head>
<body>
<h2>example_json</h2><p />
<div class="contents">contents</div>
<hr />
Jul/24/2018 AM 08:25<p />
</body>
</html>
example_json.js
// -----------------------------------------------------------------------
// example_json.js
//
// Jul/24/2018
//
// -----------------------------------------------------------------------
jQuery (function ()
{
jQuery("#outarea_aa").text ("*** example_json *** start ***")
var data_text = ""
// var file_in = "./tochigi.json"
var file_in = "./cities.json"
jQuery.getJSON (file_in,function (data_aa)
{
var str_out = ""
str_out += "<table>"
for (var key in data_aa)
{
str_out += "<tr>"
str_out += "<td>" + data_aa[key].name + "</td>"
str_out += "<td>" + data_aa[key].population + "</td>"
str_out += "<td>" + data_aa[key].date_mod + "</td>"
str_out += "</tr>"
}
str_out += "</table>"
jQuery(".contents").html (str_out)
})
.fail(function(jqXHR, textStatus, errorThrown)
{
var str_out = "<h2>Not Exist</h2>"
str_out += "<blockquote>"
str_out += file_in + "<br />"
str_out += "</blockquote>"
jQuery(".contents").html(str_out)
jQuery("#outarea_ee").text("textStatus = " + textStatus)
})
jQuery("#outarea_hh").text ("*** example_json *** end ***")
})
// -----------------------------------------------------------------------
サンプルのJSON ファイル
cities.json
{
"t0921": {
"name": "宇都宮",
"population": 68714,
"date_mod": "1950-9-24"
},
"t0922": {
"name": "小山",
"population": 29157,
"date_mod": "1950-3-15"
},
"t0923": {
"name": "佐野",
"population": 65741,
"date_mod": "1950-10-7"
},
"t0924": {
"name": "足利",
"population": 38164,
"date_mod": "1950-6-22"
},
"t0925": {
"name": "日光",
"population": 49675,
"date_mod": "1950-8-28"
},
"t0926": {
"name": "下野",
"population": 65813,
"date_mod": "1950-9-12"
}
}