leetcode: Contains Duplicate : JavaScript submission 86%+ runtime

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I did leetcode’s “Contains Duplicate” problem and surprisingly got my runtime to beat 86.89% of other JavaScript solutions.

The code uses JavaScript’s Set object which “lets you store unique values of any type, whether primitive values or object references.” The premise of the solution is that every time a value appears, we check the set to see if it exists. If not we add it to the set. If it does exist we return a true, ending the program.

An additional note, the reason that forEach would not be a good choice is that you can’t return from a forEach. So if I found in index 1 that we have a duplicate, with a for loop we can return and the function does not need to iterate over n more elements. With a forEach we would have to wait until the end of the forEach when the answer is already known

var containsDuplicate = function(nums) {
    let set = new Set()
        if(set.has(nums[i])){return true}
    return false


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