Solve - includes is not a function Error in JavaScript

Solve - includes is not a function Error in JavaScript #

The "includes is not a function" error occurs when the includes() method is called on a value that is not of type string or array. To solve the error, convert the value to a string or array before calling the method or make sure to only call the includes method on strings or arrays.

Here is an example of how the error occurs.

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const str = 1234;

// ⛔️ Uncaught TypeError: str.includes is not a function
const result = str.includes('3');

We called the includes method on a number which caused the error. The includes method is only supported on strings or arrays.

To solve the error, convert the value to a string or an array before calling the method, or only call the method if the value is of the correct type.

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// 👇️ For Strings
const num = 1234;
const result1 = num.toString().includes('3');
console.log(result1); // 👉️ true

// 👇️ For Arrays
const set = new Set(['a', 'b', 'c']);
const result2 = Array.from(set).includes('b');
console.log(result2); // 👉️ true

We converted the number to a string using the toString() method before we called the includes method.

In the second example, we used the Array.from method to convert a Set to an array before calling the includes method.

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const num = 1234;
const result1 = typeof num === 'string' ? num.includes('3') : false;
console.log(result1); // 👉️ false

// 👇️ For Arrays
const set = new Set(['a', 'b', 'c']);
const result2 = Array.isArray(set) ? set.includes('b') : false;
console.log(result2); // 👉️ false

We used the ternary operator, which is very similar to an if/else statement.

In the first example, we check if the value has a type of string. If it does, we return the result of calling the includes method, otherwise we return false.

In the second example, we check if the value is an array using the Array.isArray method.

If the value is an array, we return the result of calling the includes method, otherwise we return false.

If you have an object, there is a very good chance you have to access a specific property on the object that has a string or an array value.

Further Reading #

• Find the Odd Numbers in an Array using JavaScript
• Check if String starts with Number using JavaScript
• Get the Sum of an Array of Numbers in JavaScript
• Split a Number into an Array in JavaScript
• Filter an Array to only Numbers in JavaScript
• Check if Array contains only Numbers in JavaScript