Solve - length is not a function Error in JavaScript

Solve - length is not a function Error #

The "length is not a function" error occurs when we try to invoke the length property like a function instead of accessing it using dot notation. To solve the error, access the length property without parenthesis, e.g. arr.length.

Here are some examples of how the error occurs.

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// ⛔️ On Arrays
const arr = [1, 2];
const r1 = arr.length();

// ⛔️ Using jQuery
const boxes = $('.box');
const r2 = boxes.length();

// ⛔️ On strings
const str = 'hello';
const r3 = str.length();

To solve the error, remove the parenthesis after the length property.

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// ✅ On Arrays
const arr = [1, 2];
const r1 = arr.length;

// ✅ Using jQuery
const boxes = $('.box');
const r2 = boxes.length;

// ✅ On strings
const str = 'hello';
const r3 = str.length;

Length is a property we can access on multiple types in JavaScript, e.g. - Array.length, String.length, NodeList.length.

The length property always returns an integer with a positive sign.

The property can also be set by the user.

Here are examples of truncating an array by setting it's length property to a lower value.

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const arr = ['a', 'b', 'c'];

arr.length = 1;

console.log(arr); // 👉️ ['a']

arr.length = 0;

console.log(arr); // 👉️ []

After setting the array's length to 1, only the first element remained in the array.

And here is an example of setting an array's length to a higher value.

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const arr = ['a'];

arr.length = 3;

console.log(arr); // 👉️ ['a', , ]

console.log(arr.length); // 👉️ 3

After we set the array's length to a higher value, the array got filled with empty elements.

All of the empty elements in the array are non-iterable.

That's because there are specialized methods that allow us to manipulate an array, that work in a more predictable manner.