how to prevent duplicate in array push in angularjs

You can use arr.indexOf which returns -1 if it is not found, so you can add it then.

e.g.

if (arr.indexOf(item) == -1) {    arr.push(item);}

However, this does not work in old browsers...

JQuery has a method ($.indexOf) that works in every browser, even very old ones.

Just javascript is enough.

If an array contains the item its index is >= 0

so you can do this, if index == -1 , item does not exist in the array, so you can push unique item

if(arr.indexOf(item) == -1) {   arr.push(item);}

Edit: You asked for changing the number, this is how

var index = arr.indexOf(item);if(index > -1) { //checking if item exist in array  arr[index]++;   // you can access that element by using arr[index],                  // then change it as you want, I'm just incrementing in above example}

As what most of the answers have pointed out, you can use the Array.prototype.indexOf() method to determine if a value exists or not. In order to check for this, check the array of strings against your ng-models value property, selects.value, within the ng-change() event callback.

DEMO

Javascript

$scope.goChange = function(name, value){  if(!~arr.indexOf(value)) {          arr.push(name, value);          console.log(arr);  }};

HTML

<select ng-model="selects" ng-change="goChange(item.name, selects.value)" ng-options="i as i.value for i in options">  <option value=""></option></select>