惰性初始化_惰性对象初始化

电玩女神 2023-02-21 14:23 35阅读 0赞

惰性初始化

The Firefox DevTools underlying code, which is written with JavaScript and HTML, is a complex application. Due to the complexity and amount of work going on, the DevTools team has done everything they can to load as little as possible. Furthermore the team has a system of lazily importing and initializing objects when they're needed. I've taken a bit of time to reduce the initializer, let's take a look!

用JavaScript和HTML编写的Firefox DevTools基础代码是一个复杂的应用程序。 由于工作的复杂性和繁重的工作量，DevTools团队已尽其所能来尽可能少地加载。 此外，该团队还具有在需要时懒惰地导入和初始化对象的系统。 我花了一些时间来简化初始化程序，让我们来看一下！

The system relies on taking advantage of `Object.defineProperty`'s `get` function to initialize an object when needed:

系统依赖于利用`Object.defineProperty`的`get`函数在需要时初始化对象：

// Lazily initializes an object's property until it's used
    function lazyGet(hostObj, name, initializer) {
        let defined = false;
        Object.defineProperty(hostObj, name, {
            get: function () {
                // If not already defined, define it by executing
                // its initializer and setting it as value
                if (!defined) {
                    defined = true;
                    // Overrides the original property definition
                    // which is the initializer
                    Object.defineProperty(hostObj, name, {
                        configurable: true,
                        enumerable: true,
                        value: initializer.apply(hostObj),
                        writable: true,
                    });
                    return hostObj[name];
                }
            },
            configurable: true,
            enumerable: true
        });
    }

With the `lazyGet` function, the property you want is only initialized and processing down when its getter is called:

使用`lazyGet`函数，仅在调用其getter时初始化并处理所需的属性：

// Don't define window.myProp until someone tries to use it
    // Thus, if it's never used, it's never initialized
    lazyGet(window, "myProp", () => {
        return { message: "Hello!" };
    });
    
    // window.myProp is now undefined, since it hasn't been requested yet
    
    // Use it for something, which triggers initialization and returns its value
    console.log(window.myProp.message);
    
    // Using it again doesn't initialize again, since it was already created
    console.log(window.myProp.message);
    
    // And it can be reassigned later on:
    window.myProp = null;

Mozilla's initializer is much more complex as it also acts as a loader, but you get the idea. We always think about lazy loading resources but it's also good to think about initializing properties as they may not be needed! Keep a tiny footprint if you can!

Mozilla的初始化程序要复杂得多，因为它也可以充当加载程序，但是您可以理解。 我们总是考虑延迟加载资源，但最好考虑初始化属性，因为可能不需要它们！ 如果可以，请保留很小的空间！

> 翻译自: [https://davidwalsh.name/lazy-object-initialization][https_davidwalsh.name_lazy-object-initialization]

惰性初始化

[https_davidwalsh.name_lazy-object-initialization]: https://davidwalsh.name/lazy-object-initialization