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JavaScript: Returns true if the provided predicate function returns true for all elements in a collection, false otherwise

JavaScript fundamental (ES6 Syntax): Exercise-16 with Solution

Write a JavaScript function that returns true if the provided predicate function returns true for all elements in a collection, false otherwise.

  • Use Array.prototype.every() to test if all elements in the collection return true based on fn.
  • Omit the second argument, fn, to use Boolean as a default.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const all = (arr, fn = Boolean) => arr.every(fn);
console.log(all([4, 2, 3], x => x > 1)); 
console.log(all([4, 2, 3], x => x < 1));
console.log(all([1, 2, 3])); 

Sample Output:

true
false
true

Flowchart:

flowchart: Returns true if the provided predicate function returns true for all elements in a collection, false otherwise

Live Demo:

See the Pen javascript-basic-exercise-1-16 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to return the minimum-maximum value of an array, after applying the provided function to set comparing rule.
Next: Write a JavaScript program to split values of two given arrays into two groups. If an element in filter is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.

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JavaScript: Tips of the Day

How to remove a specific item from an array?

Find the index of the array element you want to remove using indexOf, and then remove that index with splice.

The splice() method changes the contents of an array by removing existing elements and/or adding new elements.

const array = [2, 5, 9];

console.log(array);

const index = array.indexOf(5);
if (index > -1) {
  array.splice(index, 1);
}

// array = [2, 9]
console.log(array);

The second parameter of splice is the number of elements to remove. Note that splice modifies the array in place and returns a new array containing the elements that have been removed.

For the reason of completeness, here are functions. The first function removes only a single occurrence (i.e. removing the first match of 5 from [2,5,9,1,5,8,5]), while the second function removes all occurrences:

function removeItemOnce(arr, value) {
  var index = arr.indexOf(value);
  if (index > -1) {
    arr.splice(index, 1);
  }
  return arr;
}

function removeItemAll(arr, value) {
  var i = 0;
  while (i < arr.length) {
    if (arr[i] === value) {
      arr.splice(i, 1);
    } else {
      ++i;
    }
  }
  return arr;
}
//Usage
console.log(removeItemOnce([2,5,9,1,5,8,5], 5))
console.log(removeItemAll([2,5,9,1,5,8,5], 5))

Ref: https://bit.ly/2N9nKRp