Exam 70-480 topic 4 question 17 discussion

Actual exam question from Microsoft's 70-480

Question #: 17
Topic #: 4

You are creating a custom function. You pass an object named testObj to the function as a parameter. You do not use inheritance through the functions.
The function must establish whether testObj inherits from another object named parentObj.
You need to ensure that the function performs as required.
Which method or operator should you add to the function?

A. parentObj.instanceof(testObj)
B. testObj.isPrototypeOf(parentObj)
C. testObj.instanceof(parentObj)
D. parentObj.isPrototypeOf(testObj)

Show Suggested Answer

Suggested Answer: B 🗳️
The isPrototypeOf() method tests for an object in another object's prototype chain.
Reference: Object.prototype.isPrototypeOf()

by MrEngineer at Nov. 28, 2019, 7:53 a.m.

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MrEngineer

Highly Voted 5 years, 7 months ago

Answer should be D https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isPrototypeOf

upvoted 10 times

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Zvonimir

Most Recent 4 years, 5 months ago

answer is C. question is does it inherit (properties, values, ...), not strictly is it one of parent's properties, so I would go with "instanceof"; https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Objects/Inheritance

upvoted 1 times

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elevator44

4 years, 11 months ago

The function must establish whether testObj inherits from another object named parentObj. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isPrototypeOf Parameters: The object whose prototype chain will be searched. In this case parameter is testObj because we are looking whether testObj inherits or not so D is correct answer.

upvoted 1 times

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KyryIx

5 years, 3 months ago

I agree with MrEngineer because <!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <title></title> </head> <body> <script> // with inheritance function parentObj(){} function testObj(){ parentObj.call(this); } testObj.prototype = new parentObj(); testObj.prototype.constructor = testObj; console.log( testObj.prototype.isPrototypeOf(parentObj) ); // false console.log( parentObj.prototype.isPrototypeOf(testObj) ); // false // with instace function parentObj(){} var testObj = new parentObj(); console.log( parentObj.prototype.isPrototypeOf(testObj) ); // true //console.log( testObj.prototype.isPrototypeOf(parentObj) ); // error </script> </body> </html> // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isPrototypeOf

upvoted 4 times

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Shapespacer

5 years, 5 months ago

Based on that website it suggests that the correct answer is B as if you look for the example of baz. Baz is the object and they search to see if bar exists within the baz prototype chain e.g Bar.prototype.isPrototyeOf(baz). this clearly shows the correct answer being B.

upvoted 4 times

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