Javascript -filtering object

Question

I am trying to do something in pure JS. I have an Object like so

var data = {
    "Something": true,
    "Something else": false,
    "Blah": false,
    "a fish ISA": true
};

What I want to do is filter anything which has true to its own Object. At the moment I am trying

var thingFunctions = Object.keys(data).filter(function(e) {
    return typeof data[e] == 'function'
});

But I think this is incorrect. How can I get the data with a value of true to its own Object?

Thanks

typeof data[e] == 'function' has nothing to with true or false booleans - you should be looking at something like typeof data[e] == 'boolean' && !!(data[e]) — somethinghere
– somethinghere, Commented Feb 9, 2016 at 15:47
@pandorym Indeed, just wanted to stay in the style provided :) — somethinghere
– somethinghere, Commented Feb 9, 2016 at 15:49

iSkore · Accepted Answer · 2016-02-09 15:51:36Z

3

So firstly you have no functions inside data, so doing a check on functions will return nothing.

var data = {
    "Something": true,
    "Something else": false,
    "Blah": false,
    "a fish ISA": true
};

var thingFunctions = Object.keys( data ).filter(function( e ) {
    return data[ e ] === true;
});

console.log( thingFunctions );

// Will result in [ 'Something', 'a fish ISA' ]

answered Feb 9, 2016 at 15:51

iSkore

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Comments

Nina Scholz · Accepted Answer · 2016-02-09 15:59:21Z

3

You were asking for an object.

I use Array.prototype.forEach() for the iteration over the keys and an empty object for the result filtered, because I can not filter objects:

var data = {
        "Something": true,
        "Something else": false,
        "Blah": false,
        "a fish ISA": true
    },
    filtered = {};

Object.keys(data).forEach(function(e) {
    if (data[e] === true) {                      // explicit testing for boolean and true!
        filtered[e] = data[e];
    }
});

document.write('<pre>' + JSON.stringify(filtered, 0, 4) + '</pre>');

edited Feb 9, 2016 at 15:59

answered Feb 9, 2016 at 15:54

Nina Scholz

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Comments

Michael Warner · Accepted Answer · 2016-02-09 16:03:58Z

3

As you want to only have all true value we can convert them to true false values by doing the following.

!!({}) // true
!!([]) // true
!!('') // false
!!(true) // true
!!(false) // false
...

With this we can see if any data type is true or false by doing the following.

var thingFunctions = Object.keys(data).filter(function(e) {
    return !!(data[e]);
});

edited Feb 9, 2016 at 16:03

answered Feb 9, 2016 at 15:55

Michael Warner

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6 Comments

somethinghere Over a year ago

This would return false when the value is true, is that correct?

somethinghere Over a year ago

But the OP wants an object where only the true objects remain, this would do the opposite. You would need a double operator: !!data[e].

Michael Warner Over a year ago

In that case you case do it again !!() this will convert it to a true false value and not convert it.

somethinghere Over a year ago

No it will not. !!(false) === false and !!(true) === true - What you are doing is !(false) === true because you invert their boolean only once. Which means you are returning false for elements that have a value of true, which means they wont be included in the eventual output of the filter.

Michael Warner Over a year ago

Is that better? I first thought he wanted the opposite values I apologize.

|

henkep · Accepted Answer · 2016-02-09 16:05:27Z

0

To get a new object instead of just an array of the keys that point to a value of true (not truthy such as 1 or "hello"):

var onlyTrues = {};

for (var prop in data) {
  if (data[prop] === true) {
    onlyTrues[prop] = data[prop];
  }
}

answered Feb 9, 2016 at 16:05

henkep

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