Check if an array contains duplicate values

I wanted to write a javascript function which checks if array contains duplicate values or not.

I have written the following code but its giving answer as "true" always.

Can anybody please tell me what am I missing.

function checkIfArrayIsUnique(myArray) 
    {
        for (var i = 0; i < myArray.length; i++) 
        {
            for (var j = 0; j < myArray.length; j++) 
            {
                if (i != j) 
                {
                    if (myArray[i] == myArray[j]) 
                    {
                        return true; // means there are duplicate values
                    }
                }
            }
        }
        return false; // means there are no duplicate values.
    }

Solution 1:

An easy solution, if you've got ES6, uses Set:

function checkIfArrayIsUnique(myArray) {
  return myArray.length === new Set(myArray).size;
}

let uniqueArray = [1, 2, 3, 4, 5];
console.log(`${uniqueArray} is unique : ${checkIfArrayIsUnique(uniqueArray)}`);

let nonUniqueArray = [1, 1, 2, 3, 4, 5];
console.log(`${nonUniqueArray} is unique : ${checkIfArrayIsUnique(nonUniqueArray)}`);

Solution 2:

This should work with only one loop:

function checkIfArrayIsUnique(arr) {
    var map = {}, i, size;

    for (i = 0, size = arr.length; i < size; i++){
        if (map[arr[i]]){
            return false;
        }

        map[arr[i]] = true;
    }

    return true;
}