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JavaScript Interview Question #43: Object.toString vs Array.toString

Coderslang: Become a Software Engineer
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Originally published at learn.coderslang.com ・1 min read

coderslang javascript interview question #43

What's the difference between Object.toString and Array.toString in JavaScript? What’s the output?

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A regular behavior of the JavaScript function Object.prototype.toString in a browser — is a string that looks like [object "TYPE"]. The part "TYPE" is substituted with the type of the Object that toString is called on. In our case, it's Array.

console.log(toStringObj.call(arr)); // [object Array]
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In the second instance, we call toString from Array. It’s not the same function as it overrides the standard implementation of Object.prototype.toString.

Array.prototype.toString returns a string that consists of all the array elements separated with commas.

console.log(toStringArr.call(arr)); // 1,2,3
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ANSWER: 2 strings will appear on the screen:

[object Array]
1,2,3
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Discussion (4)

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yohanchoidev profile image
YC John

I think this type of questions is not good interview question since mostly it tests a certain knowledge, not problem solving skill.

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coderslang profile image
Coderslang: Become a Software Engineer Author

Tests a certain knowledge (JS in this case) doesn't exclude questions related to problem solving.

For a skilled candidate it's equally important to have both.

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yohanchoidev profile image
YC John

Only if the knowledge is essential, then it makes sense. but I don't think so in this problem. That's very bad since these kind of test wastes developer's time. I can't find any point of this question. Probably, it would be better if the developer can ask himself when he is not sure. If he is not, then he will check reference.

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coderslang profile image
Coderslang: Become a Software Engineer Author • Edited

An interviewer can tell a lot about the candidate when they're presented with the question they're unfamiliar with.

Will they immediately tell you they don't know and try to use logic and a set of possible outcomes?
Will they try to blindly guess the result?
Will they just collapse and try to tell you don't anything about a proper interview?