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Salesforce JS-Dev-101 Exam - Topic 6 Question 4 Discussion
Topic #: 6
A class was written to represent items for purchase in an online store, and a second class representing items that are on sale at a discounted price. The constructor sets the name to the first value passed in. There is a new requirement for a developer to implement a description method that will return a brief description for Item and SaleItem.
01 let regItem = new Item('Scarf', 55);
02 let saleItem = new SaleItem('Shirt', 80, .1);
03 Item.prototype.description = function() { return 'This is a ' + this.name; }
04 console.log(regItem.description());
05 console.log(saleItem.description());
06
07 SaleItem.prototype.description = function() { return 'This is a discounted ' + this.name; }
What is the output when executing the code above?
Comprehensive and Detailed
Assuming SaleItem inherits from Item via prototype (e.g. SaleItem.prototype = Object.create(Item.prototype)):
Lines 01--02: create regItem and saleItem.
Line 03: define Item.prototype.description.
Now both regItem and saleItem (via inheritance) have a description method from Item.prototype.
Line 04: regItem.description() 'This is a Scarf'.
Line 05: saleItem.description() 'This is a Shirt' (same method, but this.name is 'Shirt').
Line 07: SaleItem.prototype.description = ... overrides description only for SaleItem instances going forward.
If we imagine calling regItem.description() and saleItem.description() again after line 07:
regItem.description() still uses Item.prototype.description 'This is a Scarf'.
saleItem.description() now uses SaleItem.prototype.description 'This is a discounted Shirt'.
Those four lines correspond to option B.
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