backbone js: collection event function options index undefined

Question

I tried to get index value for the model. but its returning undefined value. how to get index value once an event is triggered.

var Test=new Backbone.Collection();

Test.add({name:'gowtham',age:20});
Test.add([{name:'eswara',age:25},

{name:'sakthi',age:20}]);
console.log(JSON.stringify(Test));

Test.remove(Test.at(1));
console.log(JSON.stringify(Test));

Test.on('add',function(model, col, options) {
    console.log('added ' +model.get('name')+'at index '+ options.index);
});
Test.add({name:'ganesh',age:22});

Answer 1

In your example i do not see any try to output index of a model

Test.on('add',function(model, col, options) {
    console.log('added ' +model.get('name')+'at index '+ `options.index);`
});

maybe its just a typo.

By default backbone add event callback has this three arguments: model, collection and options and there is no index, so you have to get it by yourself

I am putting here snippet about how to get index of added model and how to add model at certain index

you still can check for additional information here: backbonejs.org

let test = new Backbone.Collection([{},{},{}]);

test.on('add', (model, collection) => {
 console.log('index is: ', collection.indexOf(model)) 
});

let model1 = test.add({});
// console: index is: 3

test.add({}, { at:0 });
// console: index is: 0

console.log('model new index: ' + test.indexOf(model1))
// console: model new index:  4

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