为什么 TypeScript 允许我添加字符串和数字?我可以预防吗? [英] Why TypeScript lets me add a string and a number? Can I prevent it?

问题描述

以下代码

let k = "1";
k += 1;
console.log(k);

使用 TypeScript 正确编译，即使在严格模式下.我原以为 tsc 会失败并出现一些错误，例如 Cannot add a string and an integer..为什么它构建成功?我可以防止这种危险行为吗?

compiles correctly using TypeScript, even in strict mode. I would have expected tsc to fail with some error like Cannot add a string and an integer.. Why does it build successfuly? Can I prevent this dangerous behavior?

推荐答案

它是有效的，因为它在 JS 中有效"在为什么某个操作不是类型错误的上下文中是一个非答案；参见 什么是所有合法的 JavaScript 都是合法的 TypeScript"?是什么意思?

"It's valid because it's valid in JS" is a non-answer in the context of why a certain operation isn't a type error; see What does "all legal JavaScript is legal TypeScript" mean?

在 JavaScript 中，像 alert("Your position in the queue is " + queuePos) 这样的代码是惯用的和常见的——不通常写成 "str" + num.toString().

In JavaScript, code like alert("Your position in the queue is " + queuePos) is idiomatic and common -- it is not commonly written as "str" + num.toString().

TypeScript 的立场是惯用的 JS 不应该导致类型错误(在实际情况下).这意味着 string + number 是允许的强制转换.

TypeScript's position is that idiomatic JS should not cause type errors (when practical). This means that string + number is an allowed coercion.

+= 应该做什么的问题是在两个选项之间进行选择的问题:

The question of what += should do is then a matter of choosing between two options:

• 一致性:x = x + y 应该与 x += y
相同
• 安全:x += y不通常出现在string和number操作数，所以应该是非法强制

• consistency: x = x + y should be identical to x += y
• safety: x += y is not commonly done between string and number operands, so should be an illegal coercion

这两种选择都是明智的和有道理的；TypeScript 碰巧选择了第一个.

Both choices are sensible and defensible; TypeScript happened to choose the first.

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