Javascript compare objects having functions using lodash isEqual

Question

how to compare two objects for equality if they have functions? lodash's isEqual works really well until functions are thrown in:

_.isEqual({
    a: 1,
    b: 2
}, {
    b: 2,    
    a: 1
});

// -> true

_.isEqual({
    a: 1,
    b: 2,
    c: function () {
        return 1;
    }
}, {
    a: 1,    
    b: 2,
    c: function () {
          return 1;
    }
});

// -> false

two anonymous function have two different prototypes, so two different objects! — user757095
– user757095, Commented May 13, 2015 at 10:37
It really depends on what you are going to compare. Best solution would be to create a hash unique per object and compare it, or, knowing the structure, make an equal function for that particular object. — Jack
– Jack, Commented May 13, 2015 at 10:40
Even though the functions do the same, they will never be equal. Do you want to ignore the functions and compare? — thefourtheye
– thefourtheye, Commented May 13, 2015 at 10:54

Adam Boduch · Accepted Answer · 2015-05-13 12:26:00Z

7

Are you sure you want to compare functions? If you only care about comparing every property that isn't a function, this is easy to do with lodash:

var o1 = { a: 1, b: 2, c: function() { return 1; } },
    o2 = { a: 1, b: 2, c: function() { return 1; } };

_.isEqual(o1, o2)
// → false

_.isEqual(_.omit(o1, _.functions(o1)), _.omit(o2, _.functions(o2)));
// → true

The functions() function returns a list of function properties, and using omit(), you can get rid of them.

answered May 13, 2015 at 12:26

Adam Boduch

11.2k3 gold badges32 silver badges38 bronze badges

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

2 Comments

Killroy Over a year ago

Since I was comparing complex objects, I needed to skip all functions: const isEqualExcludingFunctions = (a, b) => isEqualWith(a, b, (a, b) => (typeof a === 'function' || typeof b === 'function')?true:undefined); replace "||" with "&&" for a slightly stricter compare.

jcady Over a year ago

Note that this doesn't work for deep comparisons. If the function is nested, it won't be found by functions and won't be omitted.

Radivarig · Accepted Answer · 2019-08-14 12:00:38Z

6

This is what I tried:

_.isEqual(o1, o2, function(val1, val2) {
  if(_.isFunction(val1) && _.isFunction(val2)) {
    return val1.toString() === val2.toString();
  }
})

Lodash supports a customizer function which allows you to write your own equality checks. This seems to be a good enough test to see if the functions are character by character the same.

edited Aug 14, 2019 at 12:00

Radivarig

1723 silver badges12 bronze badges

answered Aug 26, 2015 at 8:12

Gaurav Agarwal

14.9k4 gold badges31 silver badges42 bronze badges

2 Comments

Radivarig Over a year ago

_.isEqualWith has this third customizer parameter lodash.com/docs/#isEqualWith

Geoff Davids Over a year ago

From the docs (helped me understand this answer better): 'If customizer returns undefined, comparisons are handled by the method instead.'

Wenfang Du · Accepted Answer · 2021-06-24 12:52:11Z

2

Try isEqualWith instead:

import { isEqualWith, isFunction } from 'lodash-es'

const o1 = { fn() {} }

const o2 = { fn() {} }

const equal = isEqualWith(o1, o2, (v1, v2) =>
  // if `customizer` returns `undefined`, comparisons are handled by the method instead
  isFunction(v1) && isFunction(v2) ? `${v1}` === `${v2}` : undefined,
)

console.log({ equal }) // { equal: true }

edited Jun 24, 2021 at 12:52

answered Jun 24, 2021 at 12:43

Wenfang Du

12k13 gold badges79 silver badges116 bronze badges

Comments

Chris Pietschmann · Accepted Answer · 2015-05-13 10:42:19Z

1

As the lodash documentation states:

Functions and DOM nodes are not supported.

https://lodash.com/docs#isEqual

answered May 13, 2015 at 10:42

Chris Pietschmann

29.9k36 gold badges124 silver badges167 bronze badges

1 Comment

Simon_Weaver Over a year ago

They've since clarified this to Functions and DOM nodes are compared by strict equality, i.e. ===. I didn't check to see if the behavior actually changed or just the comment.

Collectives™ on Stack Overflow

Javascript compare objects having functions using lodash isEqual

4 Answers 4

2 Comments

2 Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

2 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related