In JavaScript, how do I check if an array has duplicate multiple values?

Question

I'm sorry I can't speak English well.

These are my simple code with a few parameters array:

 if (link.indexOf({"x" : "1" ,  "y":"2" ,  "z": "3"}) === -1) {
    link.push({
        "x": "1",
        "y": "2",
        "z": "3"
    });    
} else {
    alert("Duplicate");
}

Used in "for" loop but not alert Duplicate.

`link.indexOf( {"x" : "1" , "y":"2" , "z": "3"}) === -1` will be always true even if the same looking object is present in array. — Maheer Ali, Dec 21 '19 at 15:09
Does the `link` array have exactly the same structure of objects? I mean having `x`, `y` and `z` properties in all? — norbitrial, Dec 21 '19 at 15:12
Not just to test these numbers manually. How can a key array be prevented from being duplicated? — Mersad Nilchy, Dec 21 '19 at 15:17
https://stackoverflow.com/questions/201183/how-to-determine-equality-for-two-javascript-objects — Jeremy J Starcher, Dec 21 '19 at 15:21

Saurabh Agrawal · Accepted Answer · 2019-12-23T09:24:26.340

You can create a separate function for this to check if element exists in list or not.

Try this:

function doesExistInList(list, obj) {
  for (let i = 0; i < list.length; i++) {
    if (list[i].x === obj.x && list[i].y === obj.y && list[i].z === obj.z) {
      return true;
    }
  }
  return false;
}

let link = [];
let obj = { "x": "1", "y": "2", "z": "3" };
if (doesExistInList(link, obj) == false) {
  link.push(obj);//insert same object to list
} else {
  alert("Duplicate");
}
console.log(link);

score 1 · Answer 2 · answered Dec 21 '19 at 15:14

JavaScript compares objects by reference -- that is, do the two objects point to the exact same spot in memory?

If so, then not only are they equal -- but they are the exact same object.

What you want is a compare-by-value -- and you'll have to do that yourself.

(You could also use the find method, but that isn't quite as supported.)

const link = [];

const testVal = {
  "x": "1",
  "y": "2",
  "z": "3"
};

const results = link.filter(k =>
  k.x === testVal.x &&
  k.y === testVal.y &&
  k.z === testVal.z);


if (results.length === 0) {
  link.push(testVal);
} else {
  alert("Duplicate");
}

console.log(link);

score 1 · Answer 3 · answered Dec 21 '19 at 15:16

If two objects have same keys and same values in javascript they are different objects. To compare two objects you need to create separate function. Then use some() to compare each object in array with given object

Note: The below doesn't work for nested object. But it will work for your given case

function compareObjs(a, b){
  if(Object.keys(a).length === Object.keys(b).length){
    for(let k in a){
      if(a[k] !== b[k]){
        return false;
      }
    }
  }
  else{
    return false;
  }
  return true;
}

const obj = {
      "x": "1",
      "y": "2",
      "z": "3"
   }

if(!link.some(a => compareObjs(obj, a))) {
   link.push(obj);
} else {
   alert("Duplicate");
}

norbitrial · Answer 4 · 2019-12-21T15:32:09.000

There are couple of options to do that. The issue is with your code even if it looks like you are trying to check with indexOf if the array contains the targeted object. The main issue is it does not check the values of the properties but the reference of the original object.

So the first solution is, checking each property of the object in a hard coded way if you have the same structure for your object:

const links = [
   {x: '2', y: '3', z: '1'},
   {x: '11', y: '32', z: '73'},
   {x: '1', y: '2', z: '3'},
   {x: '93', y: '6', z: '76'},
];

const aim = {x: '1', y: '2', z: '3'};

links.forEach(link => {
  const result = link.x === aim.x && link.y === aim.y && link.z === aim.z;  
  console.log(link, `This object has same property values as aim: ${result}`);
});

There are smarter solutions, just like getting the keys of the object what it has dynamically and comparing them by using some():

const links = [
   {x: '2', y: '3', z: '1'},
   {x: '11', y: '32', z: '73'},
   {x: '1', y: '2', z: '3'},
   {x: '93', y: '6', z: '76'},
];

const aim = {x: '1', y: '2', z: '3'};

links.forEach(link => {
  const keysOfLink = Object.keys(link);
  const keysOfAim = Object.keys(aim);
  const result = keysOfLink.length === keysOfAim.length &&
                 keysOfLink.some(key => link[key] === aim[key]);
  console.log(link, `This object has same property values as aim: ${result}`);
});

I would go with the second option, that's definitely smartest way to check.

From Array.prototype.some()'s documentation:

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.

Once in the result variable you have true value, you can push as you wanted originally.

I hope this helps!

In JavaScript, how do I check if an array has duplicate multiple values?

4 Answers4

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