TypeError: replace is not a function in JavaScript

# TypeError: replace is not a function in JavaScript

The "TypeError: replace is not a function" error occurs when we call the replace() method on a value that is not of type string.

To solve the error, convert the value to a string, or check if the value is of type string before calling the replace() method.

Here is an example of how the error occurs.

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const num = 10;

// ⛔️ Uncaught TypeError: num.replace is not a function
const result = num.replace(/[0-9]/g, '-')

We called the String.replace() method on a number so the error occurred.

# Convert the value to a String before calling replace()

To solve the error, convert the number to a string before calling the replace() method.

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const num = 10;

// ✅ call toString() first
const result = num.toString().replace(/[0-9]/g, '-');

console.log(result); // 👉️ "--"

We used the toString() method to convert the number to a string before calling replace().

You can also use the String() constructor to convert the value to a string.

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const num = 10;

const result = String(num).replace(/[0-9]/g, '-');

console.log(result); // 👉️ "--"

The String() constructor returns the string representation of the provided object.

# Check if the value is a string before calling replace()

Alternatively, you can conditionally check if the value is a string before calling the replace() method.

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const num = 12345;

const result =
  typeof num === 'string' ? num.replace(/[0-9]/g, '-') : '';

console.log(result); // 👉️ ""

We used the ternary operator to check if the num variable stores a string.

If it does, the value to the left of the comma is returned, otherwise the value to the right is returned.

You can also use a simple if statement to check if the value is of type string.

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const num = 12345;

let result = '';

if (typeof num === 'string') {
  result = num.replace(/[0-9]/g, '-');
}

console.log(result); // 👉️ ""

If the error persists, console.log the value you're calling the replace method on and use the typeof operator to check its type.

If the value is an object, there's a very good chance that you are forgetting to access a specific property, on which you need to call the replace() method.

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const obj = {
  name: 'bobby',
};

const result = obj.name.replace(/bo/, 'abc');
console.log(result); // 👉️ abcbby

The object has a name property of type string, so we had to access the property before we were able to use the String.replace() method.

The String.replace() method returns a new string with one, some, or all matches of a regular expression replaced with the provided replacement.

The method takes the following parameters:

The String.replace() method returns a new string with the matches of the pattern replaced. The method doesn't change the original string.

Strings are immutable in JavaScript.

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const num = 42;

const result = String(num).replace('4', 'four');

console.log(result); // 👉️ 'four2'