How to use JavaScript Filter function

/ #JavaScript


JavaScript Filter is a Higher-Order function and in this post I'll show you how to use it.

What is a Higher-Order function?

A higher order function is a function that operates on other functions. They can either take functions as arguments, or they can return them. In other words, either you pass inn a function or you get a function in return.

A quick example

Let's say that you have a list of products with a number of quantities in stock. We want to create a new array with all the products with zero in stock. This is how you would solve it without a higher-order function:

const products = [
	{ title: 'Banana', stock: 1 },
	{ title: 'Apple', stock: 3 },
	{ title: 'Orange', stock: 0 },
	{ title: 'Pear', stock: 0 },
	{ title: 'Pineapple', stock: 1 }
];

const outOfStock = [];

for (let i = 0; i < products.length; i++) {
	if (products[i].stock === 0) {
		outOfStock.push(products[i]);
	}
}

// Print the array

console.log(outOfStock);

This is not very elegant. Let's try if using the filter function:

const products = [
	{ title: 'Banana', stock: 1 },
	{ title: 'Apple', stock: 3 },
	{ title: 'Orange', stock: 0 },
	{ title: 'Pear', stock: 0 },
	{ title: 'Pineapple', stock: 1 }
];

const outOfStock = products.filter(product => product.stock === 1);

// Print the array

console.log(outOfStock);

As you can see, solving this using filter is very easy and it looks much better.

Questions?

If any of this was unclear, feel free to leave me a reply below! I'm also open to answer other questions about coding.


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