I am trying to create a function if an array of integers has duplicate values, so I came up with the following implementation, and it works:

const containsDuplicate = (nums) => {
    const hashTable = {}
    
    for (let num in nums) {
        const numValue = nums[num]
        if (numValue in hashTable) return true
        hashTable[numValue] = "a"
    }
    
    return false
};

But, I want to know a semantic way to implement this following ES6 style, I tried the .forEach but, I discovered that I cant break out of it.