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)}`);