javascript - JS 利用eval建構replace函數無效

Question

程式碼意義：建立一個簡單的GADERYPOLUKI解碼器

The GADERYPOLUKI is a simple substitution cypher used in scouting to encrypt messages. The encryption is based on short, easy to remember key. The key is written as paired letters, which 假 inj.

example:

encode("ABCD", "agedyropulik");             // => GBCE 

程式碼如下，我想用eval函數建構出可以替換字元的函數，但是看起來沒有用。

function decode(str,key) {

    key = key.split('')

    while (key.length>0) {
        let b = key.pop(), a = key.pop();
        eval(`str.replace(/${a}/g, "${b}")`)
        eval(`str.replace(/${a.toUpperCase()}/g, "${b.toUpperCase()}")`)
        eval(`str.replace(/${b}/g, "${a}")`)
        eval(`str.replace(/${b.toUpperCase()}/g, "${a.toUpperCase()}")`)
        console.log(a, b, str, `str.replace(/${a}/g, "${b}")`)
    }

    return str

}

console.log(decode("Hmdr nge brres", "gaderypoluki"))
console.log("Hmdr nge brres".replace(/g/g, "a"))

>>> k i Hmdr nge brres str.replace(/k/g, "i")
    l u Hmdr nge brres str.replace(/l/g, "u")
    p o Hmdr nge brres str.replace(/p/g, "o")
    r y Hmdr nge brres str.replace(/r/g, "y")
    d e Hmdr nge brres str.replace(/d/g, "e")
    g a Hmdr nge brres str.replace(/g/g, "a")
    Hmdr nge brres
    Hmdr nae brres

Answer 1

replace 不會改變原有值，而是回傳新字串。

其實你可以用 new RegExp(a, 'g') 就不需要 eval