Many popular libraries and frameworks use plug-in systems such as WordPress, jQuery, Gatsby, Eleventy, and Vue. The plug-in system allows developers to add features in a secure and scalable way, enhancing the value of core projects and building communities while reducing maintenance burdens. This article will explain its design concept by building a JavaScript plug-in system.

We will take an example of a simple JavaScript calculator called BetaCalc, with the goal of allowing other developers to add a "button" feature to it.

Initial calculator code:

 // Calculator const betaCalc = {
    currentValue: 0,

    setValue(newValue) {
        this.currentValue = newValue;
        console.log(this.currentValue);
    },

    plus(addend) {
        this.setValue(this.currentValue addend);
    },

    minus(subtrahend) {
        this.setValue(this.currentValue - subtrahend);
    }
};

// Use calculator betaCalc.setValue(3); // => 3
betaCalc.plus(3); // => 6
betaCalc.minus(2); // => 4

This calculator has limited functionality and can only display results through console.log . Next, we will add the plugin system.

The simplest plug-in system:

We first create a register method that allows developers to register plugins. This method takes the plugin, gets its exec function, and attaches it to the calculator as a new method:

 // Calculator const betaCalc = {
    // ...Other calculator code register(plugin) {
        const { name, exec } = plugin;
        this[name] = exec;
    }
};

An example of a simple "square" button plugin:

 // Define the plugin const squaredPlugin = {
    name: 'squared',
    exec: function() {
        this.setValue(this.currentValue * this.currentValue);
    }
};

// Register plugin betaCalc.register(squaredPlugin);

Plugins usually contain two parts: code and metadata (name, description, version number, dependencies, etc.). In this example, the exec function contains code and name is metadata. After registration, exec function is directly attached to betaCalc object as a method.

Now, BetaCalc has a new "squared" button:

 betaCalc.setValue(3); // => 3
betaCalc.plus(2); // => 5
betaCalc.squared(); // => 25
betaCalc.squared(); // => 625

This method is simple and easy to use, and the plug-in can be easily distributed and imported through npm. But it also has flaws: the plugin directly accesses this in betaCalc , has permission to read and write all code, and violates the principle of opening and closing. In addition, the squared function works through side effects and is not ideal.

Improved plug-in architecture:

To solve these problems, we improve the plug-in architecture:

 // Calculator const betaCalc = {
    currentValue: 0,

    setValue(value) {
        this.currentValue = value;
        console.log(this.currentValue);
    },

    core: {
        'plus': (currentVal, addend) => currentVal addend,
        'minus': (currentVal, subtrahend) => currentVal - subtrahend
    },

    plugins: {},

    press(buttonName, newVal) {
        const func = this.core[buttonName] || this.plugins[buttonName];
        this.setValue(func(this.currentValue, newVal));
    },

    register(plugin) {
        const { name, exec } = plugin;
        this.plugins[name] = exec;
    }
};

// Plugin const squaredPlugin = {
    name: 'squared',
    exec: function(currentValue) {
        return currentValue * currentValue;
    }
};

betaCalc.register(squaredPlugin);

// Use calculator betaCalc.setValue(3); // => 3
betaCalc.press('plus', 2); // => 5
betaCalc.press('squared'); // => 25
betaCalc.press('squared'); // => 625

Improvements:

1. Separate the plugin from the core method and store it in the plugins object to improve security.
2. Use the press method to find functions and call them by name, convert buttons into pure functions, simplifying API, convenient testing, and reducing coupling.

This architecture is more limited, but safer and more reliable. It may be too strict, limiting the functionality extension of the plugin. The permissions of plug-in authors need to be carefully weighed, which not only ensures the stability of the project, but also allows them to solve problems.

Further improvements:

It can be further improved: add error handling, extend plug-in functions (such as registration lifecycle callbacks, storage status, etc.), and improve plug-in registration mechanism (supports batch registration, configuration settings, etc.).

Summarize:

Building an excellent plug-in system is not easy, and requires careful consideration of various factors. Only by referring to the plug-in system of existing projects (such as jQuery, Gatsby, etc.) and JavaScript design patterns, and following software development principles (such as open and shutdown principles, loose coupling, Dimitter rules, dependency injection), can we build a plug-in system that meets all user needs in the long term. A good plug-in system can promote the prosperity of the developer community and achieve a win-win situation.

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