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JavaScript: Count the occurrences of a value in an array

JavaScript fundamental (ES6 Syntax): Exercise-70 with Solution

Write a JavaScript program to count the occurrences of a value in an array.

  • Use Array.prototype.reduce() to increment a counter each time the specific value is encountered inside the array.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);
console.log(countOccurrences([1, 1, 2, 1, 2, 3], 1));
console.log(countOccurrences([1, 1, 2, 1, 2, 3], 2));
console.log(countOccurrences([1, 1, 2, 1, 2, 3], 3));

Sample Output:

3
2
1

Pictorial Presentation:

JavaScript Fundamental: Count the occurrences of a value in an array
JavaScript Fundamental: Count the occurrences of a value in an array

Flowchart:

flowchart: Count the occurrences of a value in an array

Live Demo:

See the Pen javascript-basic-exercise-70-1 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to group the elements of an array based on the given function and returns the count of elements in each group.
Next: Write a JavaScript program to create a deep clone of an object.

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JavaScript: Tips of the Day

Converts a string to title case

Example:

const toTitleCase = str =>
  str
    .match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
    .map(x => x.charAt(0).toUpperCase() + x.slice(1))
    .join(' ');
console.log(toTitleCase('some_database_field_name')); // 'Some Database Field Name'
console.log(toTitleCase('Some label that needs to be title-cased')); // 'Some Label That Needs To Be Title Cased'
console.log(toTitleCase('some-package-name')); // 'Some Package Name'
console.log(toTitleCase('some-mixed_string with spaces_underscores-and-hyphens')); // 'Some Mixed String With Spaces Underscores And Hyphens' 

Output:

"Some Database Field Name"
"Some Label That Needs To Be Title Cased"
"Some Package Name"
"Some Mixed String With Spaces Underscores And Hyphens"