Javascript private function. OOP in JS, Part 1 : Public/Private Variables and Methods 2018-07-07

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OOP in JS, Part 1 : Public/Private Variables and Methods

javascript private function

As a final caveat: the image cache created earlier suffers from the same problem, so for the above code to work properly, the image cache must be rewritten using WeakMaps too. This is slightly less efficient than using the underscore convention, but not significantly for most applications. Using WeakMaps The techniques above are either not restrictive enough prefixes or too restrictive closures , however the recent introduction of WeakMaps provides a solution. Changing those to be public properties would allow any code to do something like gk. When a thumbnail's image goes out of scope, the WeakMap ensures that its entry in the thumbnail cache will eventually be garbage collected.

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OOP in JS, Part 1 : Public/Private Variables and Methods

javascript private function

Keeping the namespace hidden from all functions, except members of Point, effectively implements private properties. Every time the person eats or exercises, they grow a year older. This is cumbersome if the number of private properties becomes large. The person has a weight which is modified by eating tripling their weight or exercising halfing it. So each time new Person is called, new copies of makeOlder , toString , getName , eat , exercise , weigh , getRace , getAge , and muchTimePasses are created. First, it's not possible to use objects as keys.

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OOP in JS, Part 1 : Public/Private Variables and Methods

javascript private function

Consider the following example: function Point x, y { this. Using Prefixes A common technique to implement private properties is to prefix each private property name with an underscore. A wiki page containing , is available to help developers transition to the new technologies. However, the use of closures makes private properties too restrictive: since there is no way to access variables in one closure from within another closure, there is no way for objects of the same class to access each other's private properties. The above two problems are exactly what WeakMaps were designed to solve. Other people created and set to beCool would still use the original 'khakis and black shirt' clothing that Gavin eschewed later in life.


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Private Properties

javascript private function

Among other things, add-ons should not be able to access variables that are supposed to be private. I say 'something like' because I discovered that this. These changes include multiprocess Firefox e10s , sandboxing, and multiple content processes. For example, the yell method in the following class will yield different values for foo and this. Don't use these techniques to develop new add-ons.

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OOP in JS, Part 1 : Public/Private Variables and Methods

javascript private function

A better alternative is to use WeakMap objects, which solve both these problems. From WeakMap to Namespace In the previous section, a separate WeakMap was used to associate each private property with an object. This article discusses two common techniques: one using prefixes, the other closures. It is this which allows the code alert gk+' is so cool. When created, a person starts out at year 1 and a hidden maximum age is determined for that person.

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Private Properties

javascript private function

. See the for more information. Starting from , no new legacy add-ons will be accepted on addons. The second problem is more severe: the thumbnail cache maintains a strong reference to each thumbnail object, so they will never be freed, even when their corresponding image has gone out of scope. The advantage of this technique is that it offers more protection: there is no way for the user to access a private property, except by using its getter or setter function. A better solution would be to store all private properties on a single object, called a namespace, and then store the namespace as a private property on the original object.

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Private Properties

javascript private function

This is a memory leak waiting to happen. } and may invoked by code external to the object. To make the above code work, a unique identifier must be associated with each image and override its toString method. It is possible to read this section on its own, but to fully appreciate how namespaces work, and the problem they set out to solve, it is recommended to read the entire article. For example, in the above age and maxAge are private variables; age can only be accessed externally through getAge it cannot be set and maxAge cannot be read or set externally. A private property is a property that is only accessible to member functions of instances of the same class.

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OOP in JS, Part 1 : Public/Private Variables and Methods

javascript private function

Moreover, because members of Point have a reference to the internal namespace, they can access private properties on other instances of Point. Note that doing so requires making private variables public since without privileged accessor methods there would be no way to use them so the public methods can get at them. Unlike other languages, JavaScript does not have native support for private properties. The person object has a publicly accessible 'clothing' property which anyone can modify, as well as a dirtFactor which can be modified manually throwing dirt on or scrubbing it off , but which increases every time the person eats or exercises, and is reduced by the use of the shower method. When an object is used as a key, it's converted to a string using its toString method. } and may only be called by privileged methods including the object's constructor.

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