JavaScript | String includes() Method

In JavaScript, includes() method determines whether a string contains the given characters within it or not.
This method returns true if the string contains the characters, otherwise, it returns false.
Note: The includes() method is case sensitive i.e, it will treat the Uppercase characters and Lowercase characters differently.

Syntax:

string.includes(searchvalue, start)

Parameters Used:

search value: It is the string in which the search will take place.

start: This is the position from where the search will be processed
(although this parameter is not necessary if this is not mentioned
the search will begin from the start of the string).

Return Value:

Returns either a Boolean true indicating the presence or it returns a false indicating the absence.

Examples:

Input : Welcome to GeeksforGeeks.
        str.includes("Geeks");


Output : true

Explanation : Since the second parameter is not defined, the search will take place from the starting index. And it will search for Geeks, as it is present in the string, it will return a true.

Input: Welcome to GeeksforGeeks.


Output: false

Explanation : Even in this case the second parameter is not defined, so the search will take place from the starting index. But as this method is case sensitive it will treat the two strings differently, hence returning a boolean false.
Since it is case sensitive.
Codes for the above function are provided below.

Code 1:

<!DOCTYPE html> 
<html> 
<body> 
<p id="GFG"></p> 
<script> 
  
    var str = "Welcome to GeeksforGeeks."; 
    var check = str.includes("Geeks"); 
    document.getElementById("GFG").innerHTML = check; 
  
</script> 
  
</body> 
</html> 

Output : false

Code 2:

<!DOCTYPE html> 
<html> 
<body> 
<p id="GFG"></p> 
<script> 
  
    var str = "Welcome to GeeksforGeeks."; 
    var check = str.includes("geeks"); 
    document.getElementById("GFG").innerHTML = check; 
  
</script> 
  
</body> 
</html> 

Output : false

Code 3:

<!DOCTYPE html> 
<html> 
<body> 
<p id="GFG"></p> 
<script> 
  
    var str = "Welcome to GeeksforGeeks."; 
    var check = str.includes("o", 17); 
    document.getElementById("GFG").innerHTML = check; 
  
</script> 
</body> 
</html> 

Output : true

Code 4:

<!DOCTYPE html> 
<html> 
<body> 
<p id="GFG"></p> 
<script> 
  
    var str = "Welcome to GeeksforGeeks."; 
    var check = str.includes("o", 18); 
    document.getElementById("GFG").innerHTML = check; 
  
</script> 
  
</body> 
</html> 

Output : false

Exceptions :

The search will not be processed if the second parameter i.e computed index(starting index) is greater than or equal to the string length and hence return false.

<!DOCTYPE html> 
<html> 
<body> 
<p id="GFG"></p> 
<script> 
  
    var str = "Welcome to GeeksforGeeks."; 
    var check = str.includes("o", 25); 
    document.getElementById("GFG").innerHTML = check; 
  
</script> 
  
</body> 
</html> 

Output : false

If the computed index(starting index) i.e the position from which the search will begin
is less than 0, the entire array will be searched.

<!DOCTYPE html> 
<html> 
<body> 
<p id="GFG"></p> 
<script> 
  
    var str = "Welcome to GeeksforGeeks."; 
    var check = str.includes("o", -2); 
    document.getElementById("GFG").innerHTML = check; 
  
</script> 
  
</body> 
</html> 

Output : true

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