Since 2015 ECMAScript, JavaScript has gained support for the Proxy and Reflect objects giving you the ability to intercept and define custom behavior for fundamental language operations, and program in JS at the meta level.
By definition, metaprogramming is a programming technique that has the ability to use other programs and software as its own data. Proxy in the JavaScript language, on the other hand, is an ES6 concept that defines specific behaviour for fundamental operations.
Bearing the simplest definition of these two concepts, how then is meta programming implemented in JavaScript with Proxies?
How JavaScript with Proxies work
Proxy is used to wrap objects and intercept their behavior. It’s actually an ES6 concept used to define custom behavior for fundamental operations.
JavaScript with Proxies works well with defining the last item or element in an array of data. Unlike Python, JavaScript does not have a direct code that will determine the terminal element immediately.
For JavaScript, the proxy will modify the behaviour of the code. It customizes a behaviour of a code to do a particular fundamental operation, which in this place is an enumeration. With proxies in place, it delivers the needed action of the web designer.
A simple example would be creating a proxy around a string property on an object. Let’s say I have an array of strings called names.
In order to serve its purpose as a proxy, it needs to have three elements:
- Target: an object which is virtualised by the Proxie
- Handler: a Placeholder Object containing traps
- Trap: the Methods that give access to the target object
The target, obviously, is the object of which reason the proxy is created.
The handler serves as a placeholder; this is where the transition and conversion start. It contains operations and commands that shall be used by JavaScript when an operation is performed on the target. It bridges easier communication between the proxy and the target. It also makes the language easier to comprehend and work with. Moreover, the handler is responsible for defining and redefining the intercepted operations.
The traps, which are inside the handlers, constitute the methods that provide property access. Traps make the communication between targets that are both with proxies.
Metaprogramming in JavaScript with Proxies
Similar to the purpose of proxies, metaprogramming can modify how a specific set of codes work. Because of this, metaprogramming is often regarded as a magical process. The extent of the modification can vary as long as it is within the bounds of what is expected from the typical action or code.
In order to use other programs as their data, developers can either use available online tools for web scraping or make their own automation platform.
Metaprogramming in JavaScript with proxies does not alter its flow unless activated. The same can be said for unactivated proxies. The additional commands will not push into play until another command allows it. The code will flow regularly and will continue to do so, even when the command is activated in the middle of running the program.
Once the trap is carried out, it will not only affect the following commands. It will also activate starting from the source. This is possible because of reflection.
Implementing Metaprogramming in JavaScript with Proxies
- Reflection
Metaprogramming is most often referred to as magical programming. It can read, generate, analyze, transform, and modify data while running. It has the capability to manipulate language that is known as the Reflection command or Reflective Metaprogramming. This command has three sub-branches, which are (1) introspection, (2) self-modification, and (3) intercession.
Introspection, staying true to its definition, means looking within or inspecting itself. It is the command used to access the internal properties that contain low-level information of the code. Self-modification, on the other hand, is the ability to modify itself.
The intercession action shares a similar purpose with the proxies in JavaScript. It takes place in another in order to carry out an action or command. In fact, the proxy object of ES6 helps with the intercession command.
Intercession and reflection are well-established even before the development of ES6 and proxies. ES6 only made the process more readable, especially for JavaScript.
- Forwards Intercepted Operations
The proxies and metaprogramming automatically forward trapped traps from handlers to the target. Each of the intercepted traps is handled by corresponding proxies. It does not limit or bar the entire process, even if it is assigned with additional tasks on top of forwarding commands.
The reflect command makes automation possible. The command has a system, a method that allows a seamless transition from one placeholder to another. The presence of both metadata and proxy makes the entire concept easier to understand and to connect.
- Modifying through Mutation
Unlike intercession that is limited at the intersection between the target and receiver, modification changes the behavior of the target according to the needs of the recipient.
As stated above, metaprogramming can modify the behavior of a function to a certain extent.
When implemented in JavaScript with Proxy, the modification is done by creating a self overriding function. The modification can either be a simple form of mutation or a harsher type, which is similar to the given example. A simpler modification would be limiting the extent of a function while overriding it with a new function.
- Creating Proxy Databases
Creating proxy servers and backup databases is a cardinal rule in data security. Metaprogramming in JavaScript can copy and reflect the data of the program and produce another copy while analyzing it.
With the aid of web scraping tools, it is easy for a metaprogramming function to analyze and replicate the data to use as its own. And by using it as its own, it means that the new copy can be part of the software or program’s primary line of defence.
Proxy databases along with SSL certifications and code signing certificates make your software program secure than ever. No amount of effort is ever too much for security measures, especially when acquiring it becomes easier with metaprogramming.
- Extra Layer of Security
Metaprogramming and proxies provide an extra layer of protection for commands and other sensitive information that are not allowed for general disclosure. In JavaScript, underscores are used before a command to indicate that it is for internal use and disclosure only. However, for those who are well-versed in the language, it is fairly easy to change and manipulate.
With proxies, it is possible to hide commands that are meant for a few people only. Metaprogramming also allows existing data from a program to be under the proxy by reflecting the strings of information. Generally, this is a needed extra layer of protection that avoids security mistakes, especially for businesses.
- Use of Revocable Proxies
Metaprogramming and proxies provide freedom to the developer. It allows them to enhance the software as much as they want but within certain limits. Another method on how they can take advantage of this freedom is by utilizing revocable proxies.
From the name itself, revocable proxies are returned. A target, may it be a native array or even another proxy, wraps with the proxy. The handler will then be an object with properties that will describe the behaviour of the proxy when an operation or command acts on it. Once the revoke command is used, the target and handle will no longer be usable.
Revocable proxies are commonly used in running statistical methods. Changing the target of a handler becomes easier with the presence of the metadata from its original source. With the change, there is also a need to validate the new target. Metaprogramming in JavaScript with proxies also makes this method happen to like a breeze.
Conclusion
Implementing metaprogramming in JavaScript with proxies opens more doors of freedom and creativity among developers. It helps in creating a more personalized programme, and with features that are more in line with the needs of the clients. It also presents several uses that are beneficial for contemporary developers who want to do their jobs in a more time-efficient manner.