✅ Array.isArray() Polyfill

jspolyfillsmedium

The Array.isArray() method determines whether the passed value is an Array.

✅ Implementation

function customIsArray(value) {
    // Return false if the value is null or undefined
    if (value === null || value === undefined) {
        return false;
    }

    // Use Object.prototype.toString to reliably check the type of value
    // This method returns '[object Array]' for arrays
    return Object.prototype.toString.call(value) === '[object Array]';
}

Explanation:

Null and Undefined Check : The function first checks if value is null or undefined. If it is, it immediately returns false.
Reliable Type Checking : For all other values, the function uses Object.prototype.toString.call(value). This method returns a string in the format "[object Type]", where Type is the internal class of the object. For arrays, it returns "[object Array]".
Why This Works : Object.prototype.toString is a reliable way to determine the internal class of an object, which helps accurately identify arrays. This is a cross-environment solution that works similarly to Array.isArray().

Behavior:

Returns true for arrays : Works for empty arrays, populated arrays, arrays created with the Array constructor, and even Array.prototype.
Returns false for non-arrays : Includes undefined, null, objects, numbers, strings, booleans, and array-like objects such as TypedArrays.

Quick Quiz

Test your understanding with 3 quick questions

Q1Why is `Object.prototype.toString.call()` used instead of `typeof`?

Q2What does `customIsArray({ length: 3 })` return?

Q3What string does `Object.prototype.toString.call([])` return?

✅ Array.isArray() Polyfill

jspolyfillsmedium

The Array.isArray() method determines whether the passed value is an Array.

✅ Implementation

function customIsArray(value) {
    // Return false if the value is null or undefined
    if (value === null || value === undefined) {
        return false;
    }

    // Use Object.prototype.toString to reliably check the type of value
    // This method returns '[object Array]' for arrays
    return Object.prototype.toString.call(value) === '[object Array]';
}

Explanation:

Null and Undefined Check : The function first checks if value is null or undefined. If it is, it immediately returns false.
Reliable Type Checking : For all other values, the function uses Object.prototype.toString.call(value). This method returns a string in the format "[object Type]", where Type is the internal class of the object. For arrays, it returns "[object Array]".
Why This Works : Object.prototype.toString is a reliable way to determine the internal class of an object, which helps accurately identify arrays. This is a cross-environment solution that works similarly to Array.isArray().

Behavior:

Returns true for arrays : Works for empty arrays, populated arrays, arrays created with the Array constructor, and even Array.prototype.
Returns false for non-arrays : Includes undefined, null, objects, numbers, strings, booleans, and array-like objects such as TypedArrays.

Quick Quiz

Test your understanding with 3 quick questions

Q1Why is `Object.prototype.toString.call()` used instead of `typeof`?

Q2What does `customIsArray({ length: 3 })` return?

Q3What string does `Object.prototype.toString.call([])` return?

✅ Array.isArray() Polyfill

✅ Implementation

Explanation:

Behavior:

Continue Reading

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✅ Array.isArray() Polyfill

✅ Implementation

Explanation:

Behavior:

Continue Reading

🛑 AbortController: Canceling Async Operations in JavaScript

🔒 Closures in JavaScript — The Complete Guide

📦 Understanding ES6 Modules in JavaScript