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?

服务器

jQuery

MySQL

JSON

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？
EN

回答 17

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何测试字符串是否为JSON？EN

回答 17

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何测试字符串是否为JSON？
EN