const arr = [1, 5, 2, 1, 6, 2, 2, 9]; const countPairs = (arr = []) => { const { length } = arr; let count = 0; // making a shallow copy so that the original array remains unaltered const copy = arr.slice(); copy.sort((a, b) => a - b); for(let i = 0; i < length; i++){ if(copy[i] === copy[i + 1]){ i++; count++; }; }; return count; }; console.log(countPairs(arr));
| Name | Description |
|---|---|
| concat() | Joins arrays and returns an array with the joined arrays |
| constructor | Returns the function that created the Array object's prototype |
| copyWithin() | Copies array elements within the array, to and from specified positions |
| entries() | Returns a key/value pair Array Iteration Object |
| every() | Checks if every element in an array pass a test array.every(function(currentValue, index, arr), thisValue) |
| fill() | Fill the elements in an array with a static value array.fill(value, start, end) |
| filter() | Creates a new array with every element in an array that pass a test array.filter(function(currentValue, index, arr), thisValue) |
| find() | Returns the value of the first element in an array that pass a test array.find(function(currentValue, index, arr),thisValue) |
| findIndex() | Returns the index of the first element in an array that pass a test array.findIndex(function(currentValue, index, arr), thisValue) |
| forEach() | Calls a function for each array element |
| from() | Creates an array from an object |
| includes() | Check if an array contains the specified element |
| indexOf() | Search the array for an element and returns its position |
| isArray() | Checks whether an object is an array |
| join() | Joins all elements of an array into a string |
| keys() | Returns a Array Iteration Object, containing the keys of the original array |
| lastIndexOf() | Search the array for an element, starting at the end, and returns its position |
| length | Sets or returns the number of elements in an array |
| map() | Creates a new array with the result of calling a function for each array element |
| pop() | Removes the last element of an array, and returns that element |
| prototype | Allows you to add properties and methods to an Array object |
| push() | Adds new elements to the end of an array, and returns the new length |
| reduce() | Reduce the values of an array to a single value (going left-to-right) |
| reduceRight() | Reduce the values of an array to a single value (going right-to-left) |
| reverse() | Reverses the order of the elements in an array |
| shift() | Removes the first element of an array, and returns that element |
| slice() | Selects a part of an array, and returns the new array |
| some() | Checks if any of the elements in an array pass a test |
| sort() | Sorts the elements of an array |
| splice() | Adds/Removes elements from an array |
| toString() | Converts an array to a string, and returns the result |
| unshift() | Adds new elements to the beginning of an array, and returns the new length |
| valueOf() | Returns the primitive value of an array |
