How to remove duplicates from a string in JavaScript

Our task is to remove all duplicated characters from a string in JavaScript. For example, if a given string is “Hello world”, the program should return just “Helo wrd”.

Standard solution

The standard solution how to remove duplicates is to iterate string through each symbol and store into a new string all symbols that aren’t included in these new string. You can find the solution below. Actually, no extra/interesting ideas, but it works well.

const unique = (str) => {
  let resultStr = ''
  for(let i = 0; i < str.length; i++) {
    if (!resultStr.includes(str[i])) {
      resultStr += str[i]
    }
  }
  return resultStr
}
unique('abbccc') // 'abc'

Go further to a more elegant solution …

Single-line solution

Which data structure does include only unique values? Yeap, the Set. And with EcmaScript6 we don’t have to implement it by themselves. Let’s use the Set constructor instead. And even better news, as far as The set takes an iterable parameter, we can pass our string directly into it. After that, we’ll get a new Set object with unique symbols. So, at that step, we have to transform these object into an array to join them into the string.

There are several ways how to convert a Set object into an array:

• firstly, using Array.from:

const array = Array.from(mySet)

• Or more elegant way, using spreading the Set out in an array:

const array = [...mySet]

As you guessed, we’ll use the last one. Now, all we got to do is use the join method to transform an array into the string:

const unique = s => [...new Set(s)].join``

Example of use:

unique('abbccc') // 'abc'

Conclusions

We have sovled task with removing duplicates from a string in JavaScript. We’ve considered a standard solution, that can be implemented in most programming languages, without using additional data structures and special methods, and more elegant single-line solution, that requires using a Set object and spreading. If you have ideas about other ways how to remove duplicated symbol - leave them below. Thanks for reading.