The Javascript **`arr.filter()`** is used to apply a test to an array. It then returns all the values that pass this test in the form of an array.

It takes as an argument an *array* and a *function* and applies the function to each element in the array. Once done, it returns an array containing all the elements that pass the condition set by the argument function.

# Syntax
Here is the function signature for the `filter()` function in Javascript:

// function signature for the filter() method
returned_values = values.filter(function)

As described above, the `filter()` function takes two inputs.  

### Input
* **`function:`** A valid, pre-defined function. This can also be a lambda function.

* **`array:`** The array on which `filter`  function is called.

### Output
**Returned:** An array containing elements of the original array that satisfied all the conditions of the input function. 

 

# Examples

Let’s take a look at a couple of examples of how the `filter()` method works:

## 1. Using pre-defined functions

The values.filter() function is passed the function `greaterThan20()` as input parameter. 

This function checks which of the elements in the `values` array is greater than or equal to $20$. The function returns an array which is stored in the variable `filtered`.

function greaterThan20(value) {
  return value >= 20;
}

var values = [34, 19, 24, 130, 14]

var filtered = values.filter(greaterThan20);
console.log(filtered)



## 2. Using a lambda function

The values.filter() function is passed a lambda function as input parameter. 

This function checks which of the elements in the `values` array is greater than or equal to $20$. The function returns an array which is stored in the variable `filtered`.

var values = [34, 19, 24, 130, 14]

var filtered = values.filter(function(value) {
  return value >= 20;
});
console.log(filtered)

The Javascript **`arr.filter()`** is used to apply a test to an array. It then returns all the values that pass this test in the form of an array.

It takes as an argument an *array* and a *function* and applies the function to each element in the array. Once done, it returns an array containing all the elements that pass the condition set by the argument function.
<h2>Syntax</h2>
Here is the function signature for the `filter()` function in Javascript:

As described above, the `filter()` function takes two inputs.  
<h4>Input</h4>
* **`function:`** A valid, pre-defined function. This can also be a lambda function.

* **`array:`** The array on which `filter`  function is called.
<h4>Output</h4>
**Returned:** An array containing elements of the original array that satisfied all the conditions of the input function. 

 

<h2>Examples</h2>

Let’s take a look at a couple of examples of how the `filter()` method works:
<h3>1. Using pre-defined functions</h3>

The values.filter() function is passed the function `greaterThan20()` as input parameter. 

This function checks which of the elements in the `values` array is greater than or equal to $20$. The function returns an array which is stored in the variable `filtered`.


<h3>2. Using a lambda function</h3>

The values.filter() function is passed a lambda function as input parameter. 

This function checks which of the elements in the `values` array is greater than or equal to $20$. The function returns an array which is stored in the variable `filtered`.

What is the JavaScript Array filter()?

The `JavaScript arr.filter()` method returns a new array of elements passing a test function.