ECMAScript 安全赋值运算符 (?=) 提案介绍及其 Polyfill

本文介绍最新的 ECMAScript 安全赋值运算符提案以及相应的替代实现

前言

我们经常会跟 try/catch 打交道，但如果你写过 Go 或者 Rust 就会发现在这两种语言中是没有 try/catch 的，那么这些语言怎么进行错误捕获呢

• Go: Error handling

f, err := os.Open("filename.ext")
if err != nil {
    log.Fatal(err)
}
// do something with the open *File f

• Rust: ? Operator / Result Type

use std::num::ParseIntError;

fn multiply(first_number_str: &str, second_number_str: &str) -> Result<i32, ParseIntError> {
    let first_number = first_number_str.parse::<i32>()?;
    let second_number = second_number_str.parse::<i32>()?;

    Ok(first_number * second_number)
}

fn print(result: Result<i32, ParseIntError>) {
    match result {
        Ok(n)  => println!("n is {}", n),
        Err(e) => println!("Error: {}", e),
    }
}

fn main() {
    print(multiply("10", "2"));
    print(multiply("t", "2"));
}

• Swift: try? Operator

func fetchData() -> Data? {
    if let data = try? fetchDataFromDisk() { return data }
    if let data = try? fetchDataFromServer() { return data }
    return nil
}

let photo = try! loadImage(atPath: "./Resources/John Appleseed.jpg")

• Zig: try Keyword

const parseU64 = @import("error_union_parsing_u64.zig").parseU64;

fn doAThing(str: []u8) !void {
    const number = try parseU64(str, 10);
    _ = number; // ...
}

好了，以上例子仅用于体现 JavaScript 语法的简单（笑

不过也确实写 try/catch 嵌套写烦了，偶然发现了这个 ?= 提案，眼前一亮，真的简洁直观