title: How to check if a JSON string has a value in JavaScript?
body: <p>Is there is any way to check if the json string has the value(char or string)? Here is the example:</p>
  
  <pre><code>{
      "firstName": "John",
      "lastName": "Smith",
      "age": 25,
      "address": {
          "streetAddress": "21 2nd Street",
          "city": "New York",
          "state": "NY",
          "postalCode": 10021
      }
  }
  </code></pre>
  
  <p>I have to check if this json has "m". It must know that "m" exists in a value.</p>