How to Solve startsWith is not a Function in JavaScript

In this tutorial, we are going to learn about how to solve the TypeError: startsWith is not a function in JavaScript.

When we use a ‘startsWith()’ method on a value which is not a data type string we will get the following error in our console.

Example:

const value = 234;

console.log(value.startsWith('2'));

Output:

"TypeError: value.startsWith is not a function

In the example above, we are getting the error because we are using the ‘startsWith()’ method on a datetype number.

To solve the “TypeError: startsWith is not a function”, make sure to call the startsWith() method on a data type string or convert the number to string before calling the startsWith() method on it.

Here is an example:

const value = 234;

const result = value.toString().startsWith('2');
console.log(result);

Output:

True

In the example above, we first converted the given value to a string using the toString() method, then we called a startsWith() method on it.

Note: The ‘startsWith()’ method of the string checks whether it begins with a particular character or not. If it matches with the specified string it returns True otherwise it returns False.

Type checking

To avoid the run time errors, we can also check the given datatype is a string or not before calling the startsWith() method on it.

Here is an example:

const value = 234;

if(typeof value === 'string'){
    console.log(value.startsWith('2'));
}else{
    console.log('Given value is not a string');
}

Conclusion

The “TypeError: startsWith is not a function” error occurs, when we call a startsWith() method on a value which is not string. To solve the error convert the value to an string before calling the startsWith() method on it or make sure to use the startsWith() method on a valid strings.