blocks|key|401780|text|使用JSON.parse|type|unstyled|depth|inlineStyleRanges|entityRanges|data|401781|function+isJson(str)+{
++++try+{
++++++++JSON.parse(str);
++++}+catch+(e)+{
++++++++return+false;
++++}
++++return+true;
}|code-block|syntax|javascript|401782|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Use JSON.parse

<pre><code>function isJson(str) {
 try {
 JSON.parse(str);
 } catch (e) {
 return false;
 }
 return true;
}
</code></pre>

blocks|key|401996|text|此代码为JSON.parse(1234)、JSON.parse(0)、JSON.parse(false)或JSON.parse(null)，所有这些都将返回true。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|401997|function+isJson(str)+{
++++try+{
++++++++JSON.parse(str);
++++}+catch+(e)+{
++++++++return+false;
++++}
++++return+true;
}|code-block|syntax|javascript|401998|所以我用这种方式重写了代码：|401999|function+isJson(item)+{
++++item+=+typeof+item+!==+"string"
++++++++?+JSON.stringify(item)
++++++++:+item;

++++try+{
++++++++item+=+JSON.parse(item);
++++}+catch+(e)+{
++++++++return+false;
++++}

++++if+(typeof+item+===+"object"+&&+item+!==+null)+{
++++++++return+true;
++++}

++++return+false;
}|402000|测试结果：|402001|isJson+test+result|402002|entityMap|0|LINK|mutability|MUTABLE|url|http://i.stack.imgur.com/ugjdF.png^0|4|G|L|D|Z|H|1H|G|0|0|0|0|0|0|I|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1A|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1C|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1D|8|@]|D|@$9|1E|A|1F|1|1G]]|E|$]]|$1|S|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

This code is <code>JSON.parse(1234)</code> or <code>JSON.parse(0)</code> or <code>JSON.parse(false)</code> or <code>JSON.parse(null)</code> all will return true.

<pre><code>function isJson(str) {
 try {
 JSON.parse(str);
 } catch (e) {
 return false;
 }
 return true;
}
</code></pre>

So I rewrote code in this way:

<pre><code>function isJson(item) {
 item = typeof item !== "string"
 ? JSON.stringify(item)
 : item;

 try {
 item = JSON.parse(item);
 } catch (e) {
 return false;
 }

 if (typeof item === "object" &amp;&amp; item !== null) {
 return true;
 }

 return false;
}
</code></pre>

Testing result:

<a href="http://i.stack.imgur.com/ugjdF.png" rel="noreferrer">isJson test result</a>

blocks|key|401817|text|如果服务器使用JSON进行响应，那么它将使用application/json内容类型，如果它使用纯文本消息进行响应，那么它应该使用text/plain内容类型。确保服务器使用正确的content-type进行响应，并进行测试。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|401818|entityMap^0|M|G|1T|A|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

If the server is responding with JSON then it would have an <code>application/json</code> content-type, if it is responding with a plain text message then it should have a <code>text/plain</code> content-type. Make sure the server is responding with the correct content-type and test that.

blocks|key|401981|text|当使用jQuery+$.ajax()时，如果响应是JSON，则响应将具有responseJSON属性，这可以像这样测试：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|401982|if+(xhr.hasOwnProperty('responseJSON'))+{}|code-block|syntax|javascript|401983|entityMap^0|3|F|10|C|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

When using <code>jQuery $.ajax()</code> the response will have the <code>responseJSON</code> property if the response was JSON, this can be tested like this:
<pre><code>if (xhr.hasOwnProperty('responseJSON')) {}
</code></pre>

blocks|key|616835|text|var+parsedData;

try+{
++++parsedData+=+JSON.parse(data)
}+catch+(e)+{
++++//+is+not+a+valid+JSON+string
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|616836|但是，我建议您的http调用/服务应始终返回相同格式的数据。因此，如果出现错误，那么应该有一个JSON对象来包装这个错误：|unstyled|616837|{"error"+:+{+"code"+:+123,+"message"+:+"Foo+not+supported"+}+}+|616838|并且可以使用HTTP状态以及5xx代码。|616839|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>var parsedData;

try {
 parsedData = JSON.parse(data)
} catch (e) {
 // is not a valid JSON string
}
</code></pre>

However, I will suggest to you that your http call / service should return always a data in the same format. So if you have an error, than you should have a JSON object that wrap this error:

<pre><code>{"error" : { "code" : 123, "message" : "Foo not supported" } } 
</code></pre>

And maybe use as well as HTTP status a 5xx code.

blocks|key|616947|text|我喜欢最好的答案，但是如果它是一个空字符串，它会返回true。所以这里有个解决办法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|616948|function+isJSON(MyTestStr){
++++try+{
++++++++var+MyJSON+=+JSON.stringify(MyTestStr);
++++++++var+json+=+JSON.parse(MyJSON);
++++++++if(typeof(MyTestStr)+==+'string')
++++++++++++if(MyTestStr.length+==+0)
++++++++++++++++return+false;
++++}
++++catch(e){
++++++++return+false;
++++}
++++return+true;
}|code-block|syntax|javascript|616949|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I like best answer but if it is an empty string it returns true. So here's a fix:

<pre><code>function isJSON(MyTestStr){
 try {
 var MyJSON = JSON.stringify(MyTestStr);
 var json = JSON.parse(MyJSON);
 if(typeof(MyTestStr) == 'string')
 if(MyTestStr.length == 0)
 return false;
 }
 catch(e){
 return false;
 }
 return true;
}
</code></pre>

blocks|key|616909|text|好吧..。这取决于您接收数据的方式。我认为服务器正在使用JSON格式的字符串进行响应(例如，使用PHP中的json_encode()+)。如果您正在使用JSON并将响应数据设置为JQuery格式，而它是一个格式错误的JSON，这将产生一个错误：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|616910|$.ajax({
++type:+'POST',
++url:+'test2.php',
++data:+"data",
++success:+function+(response){

++++++++//Supposing+x+is+a+JSON+property...
++++++++alert(response.x);

++},
++dataType:+'json',
++//Invalid+JSON
++error:+function+(){+alert("error!");+}
});|code-block|syntax|javascript|616911|但是，如果您使用类型响应作为文本，则需要使用$.parseJSON。根据jquery站点：“传入格式错误的JSON字符串可能会导致抛出异常”。因此，您的代码将是：|616912|$.ajax({
++type:+'POST',
++url:+'test2.php',
++data:+"data",
++success:+function+(response){

++++++++try+{
++++++++++++parsedData+=+JSON.parse(response);
++++++++}+catch+(e)+{
++++++++++++//+is+not+a+valid+JSON+string
++++++++}

++},
++dataType:+'text',
});|616913|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Well... It depends the way you are receiving your data. I think the server is responding with a JSON formated 
string (using json_encode() in PHP,e.g.). If you're using JQuery post and set response data to be a JSON format and it is a malformed JSON, this will produce an error:

<pre><code>$.ajax({
 type: 'POST',
 url: 'test2.php',
 data: "data",
 success: function (response){

 //Supposing x is a JSON property...
 alert(response.x);

 },
 dataType: 'json',
 //Invalid JSON
 error: function (){ alert("error!"); }
});
</code></pre>

But, if you're using the type response as text, you need use $.parseJSON. According jquery site: 
"Passing in a malformed JSON string may result in an exception being thrown". Thus your code will be:

<pre><code>$.ajax({
 type: 'POST',
 url: 'test2.php',
 data: "data",
 success: function (response){

 try {
 parsedData = JSON.parse(response);
 } catch (e) {
 // is not a valid JSON string
 }

 },
 dataType: 'text',
});
</code></pre>

blocks|key|402116|text|我只用了两行代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|402117|var+isValidJSON+=+true;
try+{+JSON.parse(jsonString)+}+catch+{+isValidJSON+=+false+}|code-block|syntax|javascript|402118|就这样!|402119|但请记住有两个陷阱：|402120|JSON.parse(null)返回null任何可以用JSON.parse()方法解析的数字或字符串。|offset|length|style|CODE|402121|JSON.parse("5")返回5|402122|JSON.parse(5)返回5|402123|让我们来玩玩代码：|402124|//+TEST+1
var+data+=+'{+"a":+1+}'

//+Avoiding+'null'+trap!+Null+is+confirmed+as+JSON.
var+isValidJSON+=+data+?+true+:+false
try+{+JSON.parse(data)+}+catch(e)+{+isValidJSON+=+false+}

console.log("data+isValidJSON:+",+isValidJSON);
console.log("data+isJSONArray:+",+isValidJSON+&&+JSON.parse(data).length+?+true+:+false);

Console+outputs:
data+isValidJSON:++true
data+isJSONArray:++false


//+TEST+2
var+data2+=+'[{+"b":+2+}]'

var+isValidJSON+=+data+?+true+:+false
try+{+JSON.parse(data2)+}+catch(e)+{+isValidJSON+=+false+}

console.log("data2+isValidJSON:+",+isValidJSON);
console.log("data2+isJSONArray:+",+isValidJSON+&&+JSON.parse(data2).length+?+true+:+false);

Console+outputs:
data2+isValidJSON:++true
data2+isJSONArray:++true


//+TEST+3
var+data3+=+'[{+2+}]'

var+isValidJSON+=+data+?+true+:+false
try+{+JSON.parse(data3)+}+catch(e)+{+isValidJSON+=+false+}

console.log("data3+isValidJSON:+",+isValidJSON);
console.log("data3+isJSONArray:+",+isValidJSON+&&+JSON.parse(data3).length+?+true+:+false);

Console+outputs:
data3+isValidJSON:++false
data3+isJSONArray:++false


//+TEST+4
var+data4+=+'2'

var+isValidJSON+=+data+?+true+:+false
try+{+JSON.parse(data4)+}+catch(e)+{+isValidJSON+=+false+}

console.log("data4+isValidJSON:+",+isValidJSON);
console.log("data4+isJSONArray:+",+isValidJSON+&&+JSON.parse(data4).length+?+true+:+false);


Console+outputs:
data4+isValidJSON:++true
data4+isJSONArray:++false


//+TEST+5
var+data5+=+''

var+isValidJSON+=+data+?+true+:+false
try+{+JSON.parse(data5)+}+catch(e)+{+isValidJSON+=+false+}

console.log("data5+isValidJSON:+",+isValidJSON);
console.log("data5+isJSONArray:+",+isValidJSON+&&+JSON.parse(data5).length+?+true+:+false);


Console+outputs:
data5+isValidJSON:++false
data5+isJSONArray:++false

//+TEST+6
var+data6;+//+undefined

var+isValidJSON+=+data+?+true+:+false
try+{+JSON.parse(data6)+}+catch(e)+{+isValidJSON+=+false+}

console.log("data6+isValidJSON:+",+isValidJSON);
console.log("data6+isJSONArray:+",+isValidJSON+&&+JSON.parse(data6).length+?+true+:+false);

Console+outputs:
data6+isValidJSON:++false
data6+isJSONArray:++false|402125|entityMap^0|0|0|0|0|0|G|I|4|R|C|0|0|F|H|1|0|0|D|F|1|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|14|8|@$M|15|N|16|O|P]|$M|17|N|18|O|P]|$M|19|N|1A|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1B|8|@$M|1C|N|1D|O|P]|$M|1E|N|1F|O|P]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1G|8|@$M|1H|N|1I|O|P]|$M|1J|N|1K|O|P]]|9|@]|A|$]]|$1|U|3|V|5|6|7|1L|8|@]|9|@]|A|$]]|$1|W|3|X|5|D|7|1M|8|@]|9|@]|A|$E|F]]|$1|Y|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|Z|$]]

I use just 2 lines to perform that:

<pre><code>var isValidJSON = true;
try { JSON.parse(jsonString) } catch { isValidJSON = false }
</code></pre>

That's all!

But keep in mind there are 2 traps: 
1. <code>JSON.parse(null)</code> returns <code>null</code> 
2. Any number or string can be parsed with <code>JSON.parse()</code> method. 
 &nbsp;&nbsp; <code>JSON.parse("5")</code> returns <code>5</code> 
 &nbsp;&nbsp; <code>JSON.parse(5)</code> returns <code>5</code> 

Let's some play on code:

<pre><code>// TEST 1
var data = '{ "a": 1 }'

// Avoiding 'null' trap! Null is confirmed as JSON.
var isValidJSON = data ? true : false
try { JSON.parse(data) } catch(e) { isValidJSON = false }

console.log("data isValidJSON: ", isValidJSON);
console.log("data isJSONArray: ", isValidJSON &amp;&amp; JSON.parse(data).length ? true : false);

Console outputs:
data isValidJSON: true
data isJSONArray: false


// TEST 2
var data2 = '[{ "b": 2 }]'

var isValidJSON = data ? true : false
try { JSON.parse(data2) } catch(e) { isValidJSON = false }

console.log("data2 isValidJSON: ", isValidJSON);
console.log("data2 isJSONArray: ", isValidJSON &amp;&amp; JSON.parse(data2).length ? true : false);

Console outputs:
data2 isValidJSON: true
data2 isJSONArray: true


// TEST 3
var data3 = '[{ 2 }]'

var isValidJSON = data ? true : false
try { JSON.parse(data3) } catch(e) { isValidJSON = false }

console.log("data3 isValidJSON: ", isValidJSON);
console.log("data3 isJSONArray: ", isValidJSON &amp;&amp; JSON.parse(data3).length ? true : false);

Console outputs:
data3 isValidJSON: false
data3 isJSONArray: false


// TEST 4
var data4 = '2'

var isValidJSON = data ? true : false
try { JSON.parse(data4) } catch(e) { isValidJSON = false }

console.log("data4 isValidJSON: ", isValidJSON);
console.log("data4 isJSONArray: ", isValidJSON &amp;&amp; JSON.parse(data4).length ? true : false);


Console outputs:
data4 isValidJSON: true
data4 isJSONArray: false


// TEST 5
var data5 = ''

var isValidJSON = data ? true : false
try { JSON.parse(data5) } catch(e) { isValidJSON = false }

console.log("data5 isValidJSON: ", isValidJSON);
console.log("data5 isJSONArray: ", isValidJSON &amp;&amp; JSON.parse(data5).length ? true : false);


Console outputs:
data5 isValidJSON: false
data5 isJSONArray: false

// TEST 6
var data6; // undefined

var isValidJSON = data ? true : false
try { JSON.parse(data6) } catch(e) { isValidJSON = false }

console.log("data6 isValidJSON: ", isValidJSON);
console.log("data6 isJSONArray: ", isValidJSON &amp;&amp; JSON.parse(data6).length ? true : false);

Console outputs:
data6 isValidJSON: false
data6 isJSONArray: false
</code></pre>

blocks|key|617826|text|这是一个代码，在伯恩的答案中做了一些小的修改。由于JSON.parse(number)运行良好，没有任何异常，因此添加了isNaN。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|617827|function+isJson(str)+{
++++try+{
++++++++JSON.parse(str);
++++}+catch+(e)+{
++++++++return+false;
++++}
++++return+isNaN(str);
}|code-block|syntax|javascript|617828|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here is a code with some minor modification in Bourne's answer.
As JSON.parse(number) works fine without any exception so added isNaN.

<pre><code>function isJson(str) {
 try {
 JSON.parse(str);
 } catch (e) {
 return false;
 }
 return isNaN(str);
}
</code></pre>

blocks|key|616870|text|您可以尝试对其进行解码并捕获exception+(原生或json2.js)：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|616871|try+{
++newObj+=+JSON.parse(myJsonString);
}+catch+(e)+{
++console.log('Not+JSON');
}|code-block|syntax|javascript|616872|但是，我建议使响应始终是有效的JSON。如果从MySQL查询中返回错误，只需返回带有错误的JSON：|616873|{"error":"The+MySQL+error+string."}|616874|然后：|616875|if+(myParsedJSON.error)+{
++console.log('An+error+occurred:+'+%2B+myParsedJSON.error);
}|616876|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/JSON/parse|1|https://github.com/douglascrockford/JSON-js/blob/master/json2.js^0|E|9|0|S|8|1|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]|$A|14|B|15|1|16]]|C|$]]|$1|D|3|E|5|F|7|17|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|18|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|19|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1A|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1B|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

You could try decoding it and catching the <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/JSON/parse" rel="nofollow">exception</a> (native or <a href="https://github.com/douglascrockford/JSON-js/blob/master/json2.js" rel="nofollow">json2.js</a>):

<pre><code>try {
 newObj = JSON.parse(myJsonString);
} catch (e) {
 console.log('Not JSON');
}
</code></pre>

However, I would suggest making the response always be valid JSON. If you get an error back from your MySQL query, simply send back JSON with the error:

<pre><code>{"error":"The MySQL error string."}
</code></pre>

And then:

<pre><code>if (myParsedJSON.error) {
 console.log('An error occurred: ' + myParsedJSON.error);
}
</code></pre>

blocks|key|617076|text|所有的json字符串都以'{‘或'’开头，并以相应的'}‘或'’结尾，所以只需要检查一下。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|617077|Angular.js是如何做到这一点的：|617078|var+JSON_START+=+/%5E\[%7C%5E\{(?!\{)/;
var+JSON_ENDS+=+{
++'[':+/]$/,
++'{':+/}$/
};

function+isJsonLike(str)+{
++++var+jsonStart+=+str.match(JSON_START);
++++return+jsonStart+&&+JSON_ENDS[jsonStart[0]].test(str);
}|code-block|syntax|javascript|617079|https://github.com/angular/angular.js/blob/v1.6.x/src/ng/http.js|offset|length|617080|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|0|1S|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|V|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|W|8|@]|9|@$K|X|L|Y|1|Z]]|A|$]]|$1|M|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|J]]]]

All json strings start with '{' or '[' and end with the corresponding '}' or ']', so just check for that. 

Here's how Angular.js does it:

<pre><code>var JSON_START = /^\[|^\{(?!\{)/;
var JSON_ENDS = {
 '[': /]$/,
 '{': /}$/
};

function isJsonLike(str) {
 var jsonStart = str.match(JSON_START);
 return jsonStart &amp;&amp; JSON_ENDS[jsonStart[0]].test(str);
}
</code></pre>

<a href="https://github.com/angular/angular.js/blob/v1.6.x/src/ng/http.js" rel="nofollow noreferrer">https://github.com/angular/angular.js/blob/v1.6.x/src/ng/http.js</a>

blocks|key|402175|text|我使用了这个(某种不同答案的混合，但不管怎样)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|402176|​|402177|const+isJSON+=+str+=>+{
++if+(typeof+str+===+'string'){
++++try+{
++++++JSON.parse(str)
++++++return+true
++++}+catch(e){
++++}
++}
++return+false
}



[null,+undefined,+false,+true,+[],+{},+
+'',+'asdf',+'{}',+'[]',+"{\"abc\":+2}","{\"abc\":+\"2\"}"]
++.map(el+=>+{
++++++console.log(`[>${el}<]+-+${isJSON(el)}`)
})

console.log('-----------------')|code-block|syntax|javascript|402178|402179|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

I used this one (kind of mix of different answers, but anyway):

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const isJSON = str =&gt; {
 if (typeof str === 'string'){
 try {
 JSON.parse(str)
 return true
 } catch(e){
 }
 }
 return false
}



[null, undefined, false, true, [], {}, 
 '', 'asdf', '{}', '[]', "{\"abc\": 2}","{\"abc\": \"2\"}"]
 .map(el =&gt; {
 console.log(`[&gt;${el}&lt;] - ${isJSON(el)}`)
})

console.log('-----------------')</code></pre>
</div>
</div>

blocks|key|617889|text|你可以尝试下面的方法，因为它也可以验证数字，null，字符串，但是上面标记的答案不能正常工作它只是修复了上面的函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|617890|function+isJson(str)+{
++try+{
++++++const+obj+=+JSON.parse(str);
++++++if+(obj+&&+typeof+obj+===+`object`)+{
++++++++return+true;
++++++}
++++}+catch+(err)+{
++++++return+false;
++++}
+++return+false;
}|code-block|syntax|javascript|617891|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can try the following one because it also validates number, null, string but the above-marked answer is not working correctly it's just a fix of the above function:
<pre><code>function isJson(str) {
 try {
 const obj = JSON.parse(str);
 if (obj &amp;&amp; typeof obj === `object`) {
 return true;
 }
 } catch (err) {
 return false;
 }
 return false;
}
</code></pre>

blocks|key|402305|text|我认为像下面这样的方法应该可以完成这项工作，它会返回解析后的JSON+(如果是有效的JSON)，所以您不需要再次调用JSON.parse。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|402306|const+tryParseJSON+=+(s)+=>+{
++++if+(!s)+return+false;

++++try+{
++++++++var+o+=+JSON.parse(s);
++++++++if+(o+&&+typeof+o+===+"object")+return+o;
++++}
++++catch+(e)+{+}

++++return+false;
};|code-block|syntax|javascript|402307|entityMap^0|1M|A|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

I think something like following method should do the job, it returns the parsed JSON (in case of valid JSON), so you don't need to call the <code>JSON.parse</code> again.
<pre class="lang-js prettyprint-override"><code>const tryParseJSON = (s) =&gt; {
 if (!s) return false;

 try {
 var o = JSON.parse(s);
 if (o &amp;&amp; typeof o === &quot;object&quot;) return o;
 }
 catch (e) { }

 return false;
};
</code></pre>

blocks|key|618018|text|如果你不介意lodash的话|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|618019|npm+i+-S+lodash|618020|const+isPlainObject+=+require("lodash/isPlainObject");+//+cjs
//+import+{isPlainObject}+from+"lodash";+//+esm
function+checkIfJSON(input)+{
++const+inputStr+=+typeof+input+===+"string"+?+input+:+JSON.stringify(input);
++try+{
++++if+(isPlainObject(JSON.parse(inputStr)))+{
++++++return+true;
++++}
++}+catch+(e)+{
++++return+false;
++}
}|code-block|syntax|javascript|618021|entityMap^0|6|6|0|0|F|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

If you don't mind <code>lodash</code>
<code>npm i -S lodash</code>
<pre><code>const isPlainObject = require(&quot;lodash/isPlainObject&quot;); // cjs
// import {isPlainObject} from &quot;lodash&quot;; // esm
function checkIfJSON(input) {
 const inputStr = typeof input === &quot;string&quot; ? input : JSON.stringify(input);
 try {
 if (isPlainObject(JSON.parse(inputStr))) {
 return true;
 }
 } catch (e) {
 return false;
 }
}
</code></pre>

blocks|key|402431|text|在JSON.parse()中，数字和布尔值被接受为有效的json，只需在解析之前添加类型验证|type|unstyled|depth|inlineStyleRanges|entityRanges|data|402432|function+isJson(str)+{

++++if(!isNaN(str)+%7C%7C+str.toString()+==+'true'+%7C%7C+str.toString()+==+'false'){
++++++++return+false;
++++}

++++try+{

++++++++JSON.parse(str);

++++}+catch+(e)+{

++++++++return+false;

++++}

++++return+true;

}|code-block|syntax|javascript|402433|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Numbers and boolean values are accepted as valid json in JSON.parse(), just add type validations before parsing
<pre><code>function isJson(str) {

 if(!isNaN(str) || str.toString() == 'true' || str.toString() == 'false'){
 return false;
 }

 try {

 JSON.parse(str);

 } catch (e) {

 return false;

 }

 return true;

}
</code></pre>

blocks|key|402139|text|除了前面的答案之外，如果您需要验证像"{}“这样的JSON格式，您可以使用以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|402140|const+validateJSON+=+(str)+=>+{
++try+{
++++const+json+=+JSON.parse(str);
++++if+(Object.prototype.toString.call(json).slice(8,-1)+!==+'Object')+{
++++++return+false;
++++}
++}+catch+(e)+{
++++return+false;
++}
++return+true;
}|code-block|syntax|javascript|402141|用法示例：|402142|validateJSON('{}')
true
validateJSON('[]')
false
validateJSON('')
false
validateJSON('2134')
false
validateJSON('{+"Id":+1,+"Name":+"Coke"+}')
true|402143|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

In addition to previous answers, in case of you need to validate a JSON format like "{}", you can use the following code:

<pre><code>const validateJSON = (str) =&gt; {
 try {
 const json = JSON.parse(str);
 if (Object.prototype.toString.call(json).slice(8,-1) !== 'Object') {
 return false;
 }
 } catch (e) {
 return false;
 }
 return true;
}
</code></pre>

Examples of usage:

<pre><code>validateJSON('{}')
true
validateJSON('[]')
false
validateJSON('')
false
validateJSON('2134')
false
validateJSON('{ "Id": 1, "Name": "Coke" }')
true
</code></pre>

I have a simple AJAX call, and the server will return either a JSON string with useful data or an error message string produced by the PHP function <code>mysql_error()</code>. How can I test whether this data is a JSON string or the error message. 

It would be nice to use a function called <code>isJSON</code> just like you can use the function <code>instanceof</code> to test if something is an Array.

This is what I want:

<pre><code>if (isJSON(data)){
 //do some data stuff
}else{
 //report the error
 alert(data);
}
</code></pre>

How to test if a string is JSON or not?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个简单的AJAX调用，服务器将返回一个包含有用数据的JSON字符串，或者返回一个由PHP函数mysql_error()生成的错误消息字符串。如何测试此数据是JSON字符串还是错误消息。使用一个名为isJSON的函数会很好，就像您可以使用函数instanceof来测试某个东西是否是一个数组一样。这就是我想要的：if (isJSON(data)){    //do some data stuff

问如何测试字符串是否为JSON？
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