Tally Javascript object property values

Question

I have several objects inside of an array in Javascript. The object looks like this:

        model: [
            {
                category: 'Media',
                value: '',
                checked: false
            },
            {
                category: 'Entertainment',
                value: '',
                checked: false
            },
            {
                category: 'Music',
                value: '',
                checked: false
            },
            {
                category: 'Theater',
                value: '',
                checked: false
            }
        ]

I want to loop through this array of objects, and tally up the number of checked: true values there are. If all of them equal true, I want to run a function. How do I go about seeing if all of the checked values are equal to true?

Checking if all of them are true the ES6 way: model.every(a=>a.checked). — Sebastian Simon
– Sebastian Simon, Commented May 19, 2015 at 1:22
@Xufox, or model.every(function (item) { return item.checked }) for non-ES6 browsers — royhowie
– royhowie, Commented May 19, 2015 at 1:25

Community · Accepted Answer · 2017-05-23 12:23:34Z

2

The easiest way to do this would be to use Array.prototype.reduce:

var aggregate = function (arr) {
    return arr.reduce(function (p, c) {
        return c.checked ? p + 1 : p;
    }, 0);
}

if (aggregate(model) === model.length) {
    // call your function
}

edit

As pointed out by @Bergi, it's faster to use the Array.prototype.every solution from the comments above, since .every terminates on the first instance the callback returns false:

var allChecked = function (arr) {
    return arr.every(function (item) {
        return item.checked;
    });
}

if (allChecked(model)) {
    // call your function
}

Although, if you're after performance, it's even faster to use a for-loop:

var allChecked = function (arr) {
    for (var i = arr.length; --i;)
        if (!arr[i].checked) return false;
    return true;
}

edited May 23, 2017 at 12:23

CommunityBot

11 silver badge

answered May 19, 2015 at 1:20

royhowie

11.2k14 gold badges54 silver badges67 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Bergi Over a year ago

Ouch, no. Not the easiest for sure (and not performant either). Why not use .every as you already suggested in the comments?

royhowie Over a year ago

@Bergi .reduce has the effect of returning the number of items where item.checked === true, instead of just a binary true/false, which could be of use to the OP

Bergi Over a year ago

OP did not mention counting? Yes, if he needs the number, then one would use reduce, but to determine "whether all of them equal true", everyis the appropriate tool.

royhowie Over a year ago

@Bergi also added a for-loop solution, since that yields the best performance

vol7ron Over a year ago

@royhowie for-loop is faster for now. every() is still kind of new and likely to be optimized at some point

vol7ron · Accepted Answer · 2015-05-19 02:58:51Z

As Xufox and royhowie suggested, every() is the optimum choice:

obj.model.every(val=>val.checked); // ES6
obj.model.every(function(val){ return val.checked; }); //ES5.1+

If you wanted to play with prototypes:

Array.prototype.countWhenField = function(field){this._field=field; return this};
Array.prototype.isEqualTo = function(val){
    var arr = this,
        fld = this._field;

    // using reduce() here as an example, but can use every()
    return arr.reduce(function (prev, curr) {
        return curr[fld] == val ? prev + 1 : prev;
    },0);
};

var obj = { 
  model : [
            {
                category: 'Media',
                value: '',
                checked: true
            },
            {
                category: 'Entertainment',
                value: '',
                checked: true
            },
            {
                category: 'Music',
                value: '',
                checked: false
            },
            {
                category: 'Theater',
                value: '',
                checked: true
            }
          ]
};

console.log(
  obj.model.countWhenField('checked').isEqualTo(true), // 3
  obj.model.length                                     // 4
);

Advice is to stay away from prototypes for various reasons (especially don't prototype the base Object or Array class). The above is a horrible example and should not by any means be used in production code (too many issues to point out in a short time).

It is important to note that the above is only a quick example to demonstrate how you can make something more english (e.g., arr.countWhenField('checked').isEqualTo(true) == arr.length).

Collectives™ on Stack Overflow

Tally Javascript object property values

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related