使用 toUpperCase 更改为 .length？

Question

我在一个 jQuery 插件中发现了这一行：

node.data.substr(0, pos).toUpperCase().length - node.data.substr(0, pos).length

据我所知，这应该始终为零，因为唯一的区别是toUpperCase()，它不应该改变字符串的长度。

这里发生了什么？

Answer 1

信不信由你，有些字符转换成大写后会变成多个字符。

例如，有一组看起来像两个字母的特殊字符。其中之一是Latin Small Ligature FI，它的存在是因为一种称为“连字”的印刷术。 “FF”、“FL”、“FFI”和“FFL”也有特殊字符。这些将变成来自.toUppercase() 的 2 或 3 个字符。

另一个例子是德语字母eszett。虽然an uppercase version exists 并于 2017 年获得德语正字法委员会的正式批准，但所有浏览器仍将单个字母“ß”转换为两个字母“SS”。

测试程序：

function countUpperDiff(input) {
  console.log((input.toUpperCase().length - input.length) + ": " + input + " → " + input.toUpperCase());
}

console.log("This program prints how many characters longer the uppercase version becomes, followed by a before-and-after view.");

console.log("Some typographic ligatures exist in lowercase, but not uppercase.")
countUpperDiff("fix");
countUpperDiff("fix");
countUpperDiff("fly");
countUpperDiff("fly");
countUpperDiff("off");
countUpperDiff("off");
countUpperDiff("affix");
countUpperDiff("affix");
countUpperDiff("raffle");
countUpperDiff("raffle");

console.log("\nThe German letter ß is NOT converted into the capital letter ẞ, but into SS. This all-caps conversion is a problem for some words:")
countUpperDiff("in massen");
countUpperDiff("in maßen");
console.log("The first one means \"in massive amounts\", while the second one means \"in moderate amounts\".")

输出：

This program prints how many characters longer the uppercase version becomes, followed by a before-and-after view.
Some typographic ligatures exist in lowercase, but not uppercase.
0: fix → FIX
1: fix → FIX
0: fly → FLY
1: fly → FLY
0: off → OFF
1: off → OFF
0: affix → AFFIX
2: affix → AFFIX
0: raffle → RAFFLE
2: raffle → RAFFLE

The German letter ß is NOT converted into the capital letter ẞ, but into SS. This is a problem for some words:
0: in massen → IN MASSEN
1: in maßen → IN MASSEN
The first one means "in massive amounts", while the second one means "in moderate amounts".

Answer 2

一些 Unicode 字符，尤其是连字，在转换为大写时会出现问题，因为它们没有对应的字符，而是可能被转换为 2 个字符。

代码示例：

var lowerChar = '\uFB00';
console.log("lowercase: ", lowerChar, "length: ", lowerChar.length);
var upperChar = lowerChar.toUpperCase();
console.log("uppercase: ", upperChar, "length: ", upperChar.length);