Create object from another one using filter function

Question

I'm trying to create an array of objects using an array of objects. My first array is like that :

And I want to create an object list with only an id, a name and a task. This is what i do actually, but it doesn't work :

var lists = data.filter(l => {
            return new ListModel(l.listId, l.listName, 'todo');
});

The ListModel object is :

class ListModel {
    constructor(id, name, tasks) {
        this.id = id;
        this.name = name;
        this.tasks = tasks;
    }

    setId(id) {
        this.id = id;
    }

    setName(name) {
        this.name = name;
    }

    setTask(task) {
        this.task = task;
    }
}

Can you post your full data object please - even a link to an offsite resource (JSFiddle, Codepen) would be preferable to an image. — Jack Bashford
– Jack Bashford, Commented Dec 27, 2018 at 21:55

Ben · Accepted Answer · 2018-12-27 21:45:13Z

1

The filter() function is more-so utilized for returning an array based upon some search criteria, similar to a WHERE clause. What you want is to utilize is the map() function using something like this:

var lists = data.map(l => {
    return new ListModel(l.listId, l.listName, 'todo');
});

answered Dec 27, 2018 at 21:45

Ben

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Comments

Nelson Teixeira · Accepted Answer · 2018-12-27 21:43:51Z

1

Use .map instead of .filter:

var lists = data.map(l => {
            return new ListModel(l.listId, l.listName, 'todo');
});

filter is for filtering elements, and the return value is taken as a boolean value for this. So in your case all elements will be validated because a new object is allways a truthy value, and you'll get a equal array.

Edit your question with the original array in text format and I'll create a working example for you.

answered Dec 27, 2018 at 21:43

Nelson Teixeira

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Comments

Joel Brewer · Accepted Answer · 2018-12-27 21:45:14Z

1

I think you want the map() function: https://www.w3schools.com/jsref/jsref_map.asp

Something like this:

const newData = data.map( item => {
  return {
    item.listId,
    item.listName,
    'todo',
  }
})

answered Dec 27, 2018 at 21:45

Joel Brewer

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Comments

varoons · Accepted Answer · 2018-12-27 21:45:16Z

1

Use map instead of filter.

Filter creates a new array with all elements that pass the test implemented by the provided function/expression.

answered Dec 27, 2018 at 21:45

varoons

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Comments

Jack Bashford · Accepted Answer · 2018-12-27 21:47:48Z

1

You're currently using Array.prototype.filter(), which removes non-matching elements from the current array. What you want to do, as far as I can tell, is use Array.prototype.map() to create a new array based upon the ListModel object. Here's how you'd do it:

var lists = data.map(l => new ListModel(l.listId, l.listName, "todo"));

answered Dec 27, 2018 at 21:47

Jack Bashford

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