JavaScript | Check if a key exists inside a JSON object

Given a JSON Object, the task is to check whether a key exists in Object or not using JavaScript. We’re going to discuss few methods.

hasOwnProperty()
This method returns a boolean denoting whether the object has the defined property as its own property (as opposed to inheriting it).
Syntax:
```
obj.hasOwnProperty(prop)
```
Parameters:
- prop: This parameter is required. It specifies the string name or Symbol of the property to check.
Return value:
It return a boolean denoting if the object has the specified property as own property.

Example 1: This example checks for prop_1 of the obj by using hasOwnProperty property.

<!DOCTYPE HTML> 
<html> 
  
<head> 
    <title> 
        JavaScript  
      | Check if a key exists inside a JSON object. 
    </title> 
</head> 
  
<body style="text-align:center;" 
      id="body"> 
    <h1 style="color:green;">   
            GeeksForGeeks   
        </h1> 
    <p id="GFG_UP" 
       style="font-size: 15px;  
              font-weight: bold;"> 
    </p> 
    <button onclick="gfg_Run()"> 
        check 
    </button> 
    <p id="GFG_DOWN"
       style="color:green;  
              font-size: 20px; 
              font-weight: bold;"> 
    </p> 
    <script> 
        var el_up =  
            document.getElementById("GFG_UP"); 
        var el_down = 
            document.getElementById("GFG_DOWN"); 
        
        var obj = { 
            prop_1: "val_1", 
            prop_2: "val_2", 
            prop_3: "val_3", 
            prop_4: "val_4", 
        }; 
        el_up.innerHTML = JSON.stringify(obj); 
  
        function gfg_Run() { 
            ans = ""; 
            var prop = 'prop_1'; 
            if (obj.hasOwnProperty(prop)) { 
                ans = "var 'obj' has " + prop + " property"; 
            } else { 
                ans = "var 'obj' has not " + prop + " property"; 
            } 
            el_down.innerHTML = ans; 
        } 
    </script> 
</body> 
  
</html> 

Output:

Before clicking on the button:
After clicking on the button:

Example 2: This example checks for pro_1 of the obj by simple array access.

<!DOCTYPE HTML> 
<html> 
  
<head> 
    <title> 
        JavaScript  
      | Check if a key exists inside a JSON object. 
    </title> 
</head> 
  
<body style="text-align:center;"
      id="body"> 
    <h1 style="color:green;">   
            GeeksForGeeks   
        </h1> 
    <p id="GFG_UP" 
       style="font-size: 15px; 
              font-weight: bold;"> 
    </p> 
    <button onclick="gfg_Run()"> 
        check 
    </button> 
    <p id="GFG_DOWN"
       style="color:green; 
              font-size: 20px; 
              font-weight: bold;"> 
    </p> 
    <script> 
        var el_up =  
            document.getElementById("GFG_UP"); 
        var el_down =  
            document.getElementById("GFG_DOWN"); 
        var obj = { 
            prop_1: "val_1", 
            prop_2: "val_2", 
            prop_3: "val_3", 
            prop_4: "val_4", 
        }; 
        el_up.innerHTML =  
          JSON.stringify(obj); 
  
        function gfg_Run() { 
            ans = ""; 
            var prop = 'pro_1'; 
            if (obj[prop]) { 
                ans = "var 'obj' has " + prop + " property"; 
            } else { 
                ans = "var 'obj' has not " + prop + " property"; 
            } 
            el_down.innerHTML = ans; 
        } 
    </script> 
</body> 
  
</html> 

Output:

Before clicking on the button:
After clicking on the button:

My Personal Notes

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