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JavaScript: Group the elements into two arrays, depending on the provided function's truthiness for each element

JavaScript fundamental (ES6 Syntax): Exercise-168 with Solution

Write a JavaScript program to group the elements into two arrays, depending on the provided function's truthiness for each element.

  • Use Array.prototype.reduce() to create an array of two arrays.
  • Use Array.prototype.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const partition = (arr, fn) =>
  arr.reduce(
    (acc, val, i, arr) => {
      acc[fn(val, i, arr) ? 0 : 1].push(val);
      return acc;
    },
    [[], []]
  );
const users = [{ user: 'barney', age: 36, active: false }, { user: 'fred', age: 40, active: true }];
partition(users, o => o.active);
console.log(users);

Sample Output:

[{"user":"barney","age":36,"active":false},{"user":"fred","age":40,"active":true}]

Flowchart:

flowchart: Group the elements into two arrays, depending on the provided function's truthiness for each element

Live Demo:

See the Pen javascript-basic-exercise-168-1 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to calculate how many numbers in the given array are less or equal to the given value using the percentile formula.
Next: Write a JavaScript program to create a function that invokes fn with partials appended to the arguments it receives.

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JavaScript: Tips of the Day

How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes:

const string = "foo";
const substring = "oo";

console.log(string.includes(substring));

includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:

var string = "foo";
var substring = "oo";

console.log(string.indexOf(substring) !== -1);

Ref: https://bit.ly/3fFFgZv