JavaScript: Takes a predicate and array, like Array.filter(), but only keeps x if pred(x) returns false

JavaScript: Exercise-155 with Solution

Filter Where Predicate is False

Write a JavaScript program that takes a predicate and an array, like Array.filter(), but only keeps x if pred(x) returns false.

Filters an array's values based on a predicate function, returning only values for which the predicate function returns false.

• Use Array.prototype.filter() in combination with the predicate function, pred, to return only the values for which it returns false.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
// Define a function 'reject' that filters elements from an array based on a provided predicate function
const reject = (pred, array) => 
  // Filter the array using the negation of the predicate function
  array.filter((...args) => !pred(...args));

// Test the 'reject' function with a predicate function and an array
console.log(reject(x => x % 2 === 0, [1, 2, 3, 4, 5])); // Output: [1, 3, 5]
console.log(reject(word => word.length > 4, ['Apple', 'Pear', 'Kiwi', 'Banana'])); // Output: ['Pear', 'Kiwi']

Output:

[1,3,5]
["Pear","Kiwi"]

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-155-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that replicates Array.filter() but only includes elements for which the predicate returns false.
• Write a JavaScript function that inverts a filtering predicate and returns an array of elements failing the test.
• Write a JavaScript program that processes an array to return only those items that do not satisfy a provided condition.
• Write a JavaScript function that filters an array for elements where a given function returns false and then logs the result.

Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to create an object composed of the properties the given function returns falsey for. The function is invoked with two arguments: (value, key).
Next: Write a JavaScript program to apply a function against an accumulator and each element in the array (from left to right), returning an array of successively reduced values.