2.8 KiB
| id | title | challengeType | forumTopicId |
|---|---|---|---|
| 587d7db2367417b2b2512b8a | Use Closure to Protect Properties Within an Object from Being Modified Externally | 1 | 18234 |
Description
In the previous challenge, bird had a public property name. It is considered public because it can be accessed and changed outside of bird's definition.
bird.name = "Duffy";
Therefore, any part of your code can easily change the name of bird to any value. Think about things like passwords and bank accounts being easily changeable by any part of your codebase. That could cause a lot of issues.
The simplest way to make this public property private is by creating a variable within the constructor function. This changes the scope of that variable to be within the constructor function versus available globally. This way, the variable can only be accessed and changed by methods also within the constructor function.
function Bird() {
let hatchedEgg = 10; // private variable
/* publicly available method that a bird object can use */
this.getHatchedEggCount = function() {
return hatchedEgg;
};
}
let ducky = new Bird();
ducky.getHatchedEggCount(); // returns 10
Here getHatchedEggCount is a privileged method, because it has access to the private variable hatchedEgg. This is possible because hatchedEgg is declared in the same context as getHatchedEggCount. In JavaScript, a function always has access to the context in which it was created. This is called closure.
Instructions
weight is declared in the Bird function so it is a private variable. Then, create a method getWeight that returns the value of weight 15.
Tests
tests:
- text: The <code>weight</code> property should be a private variable and should be assigned the value of <code>15</code>.
testString: assert(code.match(/(var|let|const)\s+weight\s*\=\s*15\;?/g));
- text: Your code should create a method in <code>Bird</code> called <code>getWeight</code> that returns the value of the private variable <code>weight</code>.
testString: assert((new Bird()).getWeight() === 15);
- text: Your <code>getWeight</code> function should return the private variable <code>weight</code>.
testString: assert(code.match(/((return\s+)|(\(\s*\)\s*\=\>\s*))weight\;?/g));
Challenge Seed
function Bird() {
this.weight = 15;
}
Solution
function Bird() {
let weight = 15;
this.getWeight = () => weight;
}