JSON.stringify not able to compare object's function. How it work?

Question

I search on net about how to compare the Object in javascript. All solution generally focus on JSON.stringify. JSON.stringify compare the object that has only absolute property means fixed value.

The JSON.stringify() method converts a JavaScript value to a JSON string.

There are (essentially) two built-in types in JS (null and undefined are special):

Primitive types (boolean, number, string, null*, undefined*).

Reference types - except primitive all are treated as an object like function.

Why JSON.stringify is not able to compare an object that has the function?

var a = {a:'xyz',
        fun: function () { var a = 10;}};
var b = {a:'xyz',
            fun: function () { var a = 10;}};

a == b => false
a === b => false
a.fun == b.fun => false
a.a == b.a => true

I searched on net then I found JSON.stringify for object comparison.

JSON.stringify(a) === JSON.stringify(b) => true

but when I try with modified b

var b = {a:'xyz',
            fun: function () { var a = 15;}}; //change a from 10 to 15.

Now I check

JSON.stringify(a) === JSON.stringify(b) => true

How it possible and how to compare an object that has a function property?

Note that two different functions are never equal, even if they have the same content. The duplicates discuss this point further. — JJJ, May 22 '17 at 10:29
as `({}) != ({})` - there's no chance a more complex Object will compare — Jaromanda X, May 22 '17 at 10:29
@WoozyCoder I already went through these question and found the solution like `JSON.stringify` but the main issue with this it prompt `true` when I changed the function variable value. — eigenharsha, May 22 '17 at 10:30
`two different functions are never equal` - you mean objects @JJJ — Jaromanda X, May 22 '17 at 10:30
@JaromandaX Well yes, but the OP is specifically stumbling with functions so I chose to be helpful rather than pedantic. — JJJ, May 22 '17 at 10:32

score 1 · Answer 1 · answered May 22 '17 at 10:30

JSON.stringify doesn't stringify function inside the object by default. Use a replacer like

 JSON.stringify(a, function(key, val) {
    return (typeof val === 'function') ? '' + val : val;
})

var a = {a:'harsha',
        fun: function () { var a = 10;}};
var b = {a:'harsha',
            fun: function () { var a = 15;}};

console.log(JSON.stringify(a, function(key, val) {
    return (typeof val === 'function') ? '' + val : val;
}),JSON.stringify(b))

console.log(JSON.stringify(a, function(key, val) {
    return (typeof val === 'function') ? '' + val : val;
}) === JSON.stringify(b, function(key, val) {
    return (typeof val === 'function') ? '' + val : val;
}));

score 0 · Answer 2 · answered May 22 '17 at 10:30

Becouse JSON.stringify doesn't stringify functions. It takes only object parameters.

var a = {a:'harsha',
        fun: function () { var a = 10;}};
var b = {a:'harsha',
            fun: function () { var a = 15;}};

console.log(JSON.stringify(a));
console.log(JSON.stringify(b));
console.log(JSON.stringify(JSON.stringify(a) === JSON.stringify(b)));

JSON.stringify not able to compare object's function. How it work?

2 Answers2