How does js determine that a string is in JSON format?

Preface

Regarding the problem of "js determines whether a string is in JSON format", I checked a lot of information on the Internet, but I didn't find the answer I wanted.

But after seeing this post"js determines whether a string is in JSON format", suddenly an idea flashed and I thought of a very Simple solution.

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Solution

function isJSON(str) {if (typeof str == 'string') {try {var obj=JSON.parse(str);if(str.indexOf('{')>-1){return true;
                }else{return false;
                }

            } catch(e) {
                console.log(e);return false;
            }
        }return false;
}

Analysis

Like the previous post said, just simply useJSON.parse(str) cannot completely verify that a string is a string in the JSON format, there are many exceptions:

<span class="hljs-built_in">JSON.parse(<span class="hljs-string">'123'); <span class="hljs-comment">// 123</span></span></span>

<span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"> JSON.parse(<span class="hljs-string">'{}'); <span class="hljs-comment">// {}</span></span></span></span></span></span>

<span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"> JSON.parse(<span class="hljs-built_in">'true'); <span class="hljs-string">// true<span class="hljs-comment"></span></span></span></span></span></span></span></span></span>

<span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"> JSON.parse(<span class="hljs-comment">'"foo"' ); <span class="hljs-built_in">// "foo"<span class="hljs-string"><span class="hljs-comment"></span></span></span></span></span></span></span></span></span></span></span> </span>

<span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"> <span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"> JSON.parse(<span class="hljs-string">'[1, 5, "false"]'); <span class="hljs-comment">// [1, 5, "false"]<span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

<span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"> JSON.parse(<span class="hljs-comment">'null'); <span class="hljs-built_in">// null<span class="hljs-string"><span class="hljs-comment"><span class="hljs-built_in"><span class="hljs-string"><span class="hljs-comment"></span></span></span> </span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>                                                                                                                                                                                                                                             Null, Undefined.

Then we will test these types of strings.

   

<span style="font-size: 16px;"><span style="color: #0000ff;">function</span><span style="color: #000000;"> isJSON_test(str) {</span><span style="color: #0000ff;">if</span> (<span style="color: #0000ff;">typeof</span> str == 'string'<span style="color: #000000;">) {</span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {</span><span style="color: #0000ff;">var</span> obj=<span style="color: #000000;">JSON.parse(str);
                console.log(</span>'转换成功：'+<span style="color: #000000;">obj);</span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">true</span><span style="color: #000000;">;
            } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;">(e) {
                console.log(</span>'error：'+str+'!!!'+<span style="color: #000000;">e);</span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">false</span><span style="color: #000000;">;
            }
        }
        console.log(</span>'It is not a string!'<span style="color: #000000;">)
 }</span><em>　<br></em></span>

<span style="font-size: 16px;">isJSON_test('123'); //number</span><br><span style="font-size: 16px;">isJSON_test('aaaa'); //string</span><br><span style="font-size: 16px;">isJSON_test('"aaa"');</span><br><span style="font-size: 16px;">isJSON_test('true'); //布尔</span><br><span style="font-size: 16px;">isJSON_test('["1","2"]'); //数组</span><br><span style="font-size: 16px;">isJSON_test('{name:"123"}'); //对象</span><br><span style="font-size: 16px;">isJSON_test('{}'); //空对象</span><br><span style="font-size: 16px;">isJSON_test('null'); //null</span><br><span style="font-size: 16px;">isJSON_test('Undefined'); //Undefined</span><br><span style="font-size: 16px;">isJSON_test('{"name":"123"}'); //json</span><br><span style="font-size: 16px;"><em>isJSON_test('{"name":"123"，}'); //不规范的json</em></span>

 

  The test results are as follows:

 

 

  From the above test results, and Definition of JSON. We can get a rule:

If JSON.parse can be converted successfully; and the string contains {, then the string is a string in JSON format.

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