Question

How to count the duplicates in an array with JavaScript

Answer 1

const arr = ['javascript', 'typescript', 'javascript', 'node.js', 'c++', 'c++', 'c++'];
 
const count = {};
 
arr.forEach(element => {
  count[element] = (count[element] || 0) + 1;
});
 
console.log(count);
 
let i = 0;
for (let key in count) { 
    let value = count[key];
    if (value > 1) {
        console.log(key); 
        i++;
    }
}    
 
console.log("duplicates: " + i);    
    
    
    
    
/*
run:
    
{
  c++: 3,
  javascript: 2,
  node.js: 1,
  typescript: 1
}
"javascript"
"c++"
"duplicates: 2"
    
*/

 

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