How can I check if the array of objects have duplicate property values?

I need some help with iterating through array, I keep getting stuck or reinventing the wheel.

values = [
    { name: 'someName1' },
    { name: 'someName2' },
    { name: 'someName1' },
    { name: 'someName1' }
]

How could I check if there are two (or more) same name value in array? I do not need a counter, just setting some variable if array values are not unique. Have in mind that array length is dynamic, also array values.

Solution 1:

Use array.prototype.map and array.prototype.some:

var values = [
    { name: 'someName1' },
    { name: 'someName2' },
    { name: 'someName4' },
    { name: 'someName2' }
];

var valueArr = values.map(function(item){ return item.name });
var isDuplicate = valueArr.some(function(item, idx){ 
    return valueArr.indexOf(item) != idx 
});
console.log(isDuplicate);

Solution 2:

ECMA Script 6 Version

If you are in an environment which supports ECMA Script 6's Set, then you can use Array.prototype.some and a Set object, like this

let seen = new Set();
var hasDuplicates = values.some(function(currentObject) {
    return seen.size === seen.add(currentObject.name).size;
});

Here, we insert each and every object's name into the Set and we check if the size before and after adding are the same. This works because Set.size returns a number based on unique data (set only adds entries if the data is unique). If/when you have duplicate names, the size won't increase (because the data won't be unique) which means that we would have already seen the current name and it will return true.

ECMA Script 5 Version

If you don't have Set support, then you can use a normal JavaScript object itself, like this

var seen = {};
var hasDuplicates = values.some(function(currentObject) {

    if (seen.hasOwnProperty(currentObject.name)) {
        // Current name is already seen
        return true;
    }

    // Current name is being seen for the first time
    return (seen[currentObject.name] = false);
});

The same can be written succinctly, like this

var seen = {};
var hasDuplicates = values.some(function (currentObject) {
    return seen.hasOwnProperty(currentObject.name)
        || (seen[currentObject.name] = false);
});

Note: In both the cases, we use Array.prototype.some because it will short-circuit. The moment it gets a truthy value from the function, it will return true immediately, it will not process rest of the elements.

Solution 3:

In TS and ES6 you can create a new Set with the property to be unique and compare it's size to the original array.

const values = [
  { name: 'someName1' },
  { name: 'someName2' },
  { name: 'someName3' },
  { name: 'someName1' }
]

const uniqueValues = new Set(values.map(v => v.name));

if (uniqueValues.size < values.length) {
  console.log('duplicates found')
}