javascript - 在javascript中有没有类似python的 `with`语句的东西？

Question

python 中的 with 语句对于清理资源很有用，例如

with open('file.txt', 'w') as f:
   // do something with the file

代码的编写者不必担心关闭文件，因为 open 函数的编写者已经实现了必要的东西来清理文件资源。

实现此功能的 javascript 中有哪些常见模式？

Answer 1

我能够在 typescript 中快速编写类似 Python 的上下文管理器的东西。希望有人发现有帮助

interface ContextManager<T> {
    enter(): T;
    exit()
}

class With {
    private manager: ContextManager<any>;

    private constructor() {
    }

    static context(manager: ContextManager<any>) {
        const withBlock = new With();
        withBlock.manager = manager;
        return withBlock;
    }

    run(func) {
        const obj = this.manager.enter();
        func(obj);
        this.manager.exit();
    }
}

用法:

class Open implements ContextManager<string> {
    private readonly name: string;

    constructor(name: string) {
        this.name = name;
    }

    enter(): string {
        console.log("Start Context: " + this.name);
        return this.name;
    }

    exit() {
        console.log("End Context: " + this.name)
    }

}


With.context(new Open("myfile.txt")).run((file) => {
    console.log("Here I am reading off: "+ file)
})

输出:

Start Context: myfile.txt
Here I am reading off: myfile.txt
End Context: myfile.txt