Javascript Filter

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Michael Zippo 04.11.2021

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The JavaScript () filter method creates an array of elements from an existing array. The filter () method takes a callback function as an argument. This function evaluates whether an item should be added to the new list from the existing one.

If you don’t know JavaScript , you might not have heard of Javascript functions filter () and reduce (). These functions can be useful when working with a list of objects, also called an array.

If you only want to get certain values ‚Äã‚Äãfrom an array, you should be able to use the filter () JavaScript function. In this tutorial, we will see, with reference to examples, how to use the filter () function.

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A JavaScript array stores zero or more elements. The elements can be numbers, other arrays, strings, or use some other type of data. They use numbered indexes starting with " 0 " to access specific items.

Arrays allow you to store multiple values ‚Äã‚Äãin the same variable. It can help you write better and cleaner because you don’t need to write multiple variables to store your values.

Here is an example of a JavaScript array:

JavaScript filters array

The JavaScript array filter () method creates a new array based on the contents of an existing array. The filter () method evaluates a callback function on each element of an existing array. Anything that satisfies the condition of the callback function is added to a new list.

Using the filter method, we are able to retrieve the values ‚Äã‚Äãthat meet certain criteria and add them to a new array.

JavaScript array filter syntax

The filter method uses the following syntax:

This code defines an array named" newArr "based on the contents of the array "oldArr". Our callback function returns a value to the new array if a condition is met. Examples of conditions:

• element> 5
• element = = "Jessie"
• element <3

You can use JavaScript comparison operators to create your conditions. Or you can use an if statement. Using an if statement allows you to control which of the multiple values ‚Äã‚Äãis added to a new list.

Examples of JavaScript filters < / h2>

Filter a list of numbers

Let’s start with a simple example. We have a shopping list at a cafe. We want to create a new list showing purchases over $ 10 .

Our shopping list looks like this:

We can use the filter () method to retrieve purchases of value greater than $ 10:

Our program checks if a purchase is worth more than $ 10. A purchase is added to our big_purchases list if it is worth more than $ 10. Otherwise, the purchase is omitted.

The value of the big_purchases JavaScript variable is:

The filter () method returns all the elements that it exceeds in the test we have defined. This test is "item> 10". If we wanted to access each purchase, we could refer to our original "purchases" list . Our filter () method returns an array of values ‚Äã‚Äãgreater than $ 10.

Filter an array of objects

We have an array that contains the names of everyone in a school:

And if we only want to recover students who are in the first year ? Filter () makes this easier. Let’s write a function that will return all the first graders in the "students" array:

Filter () accepts one parameter. This is a function that determines what action you take on your data.