JavaScript: Different results of JSON.stringify(object) and String(object)

Question

I have an array of strings, and a productId that is a type of object

productIds = [ '61b8b4a7ebffe000ec619219', '61c08d910579b11c103ba3b5' ];

productId = 61b8b4a7ebffe000ec619219;

The productId is a value from MongoDB which the field is type Object.Schema.ObjectId

Now, I want to check if productId is in productIds. Hence, I need to convert/parse productId to string.

Why is it that the code below results in true

productIds.includes(String(productId))
productIds[0] === String(productId)

While the code below results in false

productIds.includes(JSON.stringify(productId))
productIds[0] === JSON.stringify(productId)

Here is also the output of me testing each type

[ '61b8b4a7ebffe000ec619219', '61c08d910579b11c103ba3b5' ] | 61b8b4a7ebffe000ec619219 is type of object

productIds.includes(String(orderedProduct._product) true
productIds.includes(JSON.stringify(orderedProduct._product)) false

61b8b4a7ebffe000ec619219 is a typeof object 61b8b4a7ebffe000ec619219 is a typeof string
true using string String(61b8b4a7ebffe000ec619219)
false using stringify JSON.stringify(61b8b4a7ebffe000ec619219)

productId = 61b8b4a7ebffe000ec619219 is invalid javascript. If productId is a string, then JSON.stringify() adds additional quotes around the the string. — adiga
– adiga, Commented Jul 19, 2022 at 8:20
Did you log the result of JSON.stringify? (it explicitly wraps the string in double quotes). But the point is productId (despite your incorrect typing of it here) is probably a string already. — pilchard
– pilchard, Commented Jul 19, 2022 at 8:20
Sorry for that confusion, anyway the productId is just a value from a specific property of an object returned by mongoose { ..., orderedProducts: [..., { _product: ObjectId("61b8b4a7ebffe000ec619219") }] — gggg
– gggg, Commented Jul 19, 2022 at 8:28

Quentin · Accepted Answer · 2022-07-19 08:21:53Z

2

productId = 61b8b4a7ebffe000ec619219;

That's a syntax error.

But leaving that aside:

String converts the value you pass to it into a string.

JSON.stringify converts the value you pass to it into string containing a JSON representation of that value.

In JSON, strings are delimited with ".

const data = "foo";

const string = String(data);
const json = JSON.stringify(data);

console.log(string);
console.log(json);

The differences with other data types become more pronounced:

const data = { "an": "object" };

const string = String(data);
const json = JSON.stringify(data);

console.log(string);
console.log(json);

answered Jul 19, 2022 at 8:21

Quentin

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1 Comment

gggg Over a year ago

I understand, I will keep this in mind. Thanks!

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