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 and got the error. The includes method is only supported on strings or arrays.

To solve the error, either convert the value to a string or 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

In the first example we convert the number to a string using the toString() method before calling 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

In both examples 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 on it, otherwise 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 on it, otherwise 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 value of an array or string.