How to determine equality of values of JavaScript object?

Question

In the given object all values of properties are the same.

var obj = {
    property1: 'Some Value',
    property2: 'Some Value',
    property3: 'Some Value',
    property4: 'Some Value'
}

The function checkEquality should return true if all values are the same and false otherwise.

I can do the following to achieve it:

function checkEquality () {
    var compare = obj.propery1;

    for (var key in obj) {
        if (obj[key] !== compare) {
            return false;
        }
    }

    return true;
}

But this solution by far not the best.

Nina Scholz · Accepted Answer · 2016-06-29 11:33:10Z

4

You could use Array#every for it.

The every method executes the provided callback function once for each element present in the array until it finds one where callback returns a falsy value (a value that becomes false when converted to a Boolean). If such an element is found, the every method immediately returns false. Otherwise, if callback returned a true value for all elements, every will return true. callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values.

var obj = { propery1: 'Some Value', propery2: 'Some Value', propery3: 'Some Value', propery4: 'Some Value' },
    equal = Object.keys(obj).every(function (k, i, kk) {
        return !i || obj[kk[0]] === obj[k];
    });

console.log(equal);

edited Jun 29, 2016 at 11:33

answered Jun 29, 2016 at 10:21

Nina Scholz

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1 Comment

pawel Over a year ago

I think using .some to find whether any element is different would be more optimal, since it would terminate on the first difference, thus going over every element would only be a worst-case scenario.

pawel · Accepted Answer · 2016-06-29 10:57:49Z

1

Great answer by @Nina, I'd just like to add something different using reduce and ES6 syntax:

const sameValues = (obj ) => {
    let keys = Object.keys( obj );
    let initial = obj[ keys[0] ];
    // val will be either the initial value or false
    let val = keys.reduce( (prev, cur) => ( obj[cur] === prev ? prev : false ), initial ); 
    return val === initial;
}

https://jsfiddle.net/9tb5mdoL/

answered Jun 29, 2016 at 10:57

pawel

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2 Comments

Nina Scholz Over a year ago

but reduce does not stop, if false. what if false is a value to test for?

pawel Over a year ago

1. I know :) I have commented on your answer fully aware of this disadvantage of my approach. 2. See the linked fiddle (false === false)

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