JavaScript“If 语句”不返回真值

Question

我编写了一个简单的函数，通过循环数组并比较值来检查提供的注释是否有效。代码总是返回false，我不确定为什么？item.split("/")[1] == note当我单独运行代码时，它会返回true（带有 note = "C" ），那么为什么我的函数总是返回false？const chromatic = ["A", "A#/Bb", "B/Cb", "B#/C", "C#/Db", "D", "D#/Eb", "E", "E#/Fb", "F", "F#/Gb", "G", "G#/Ab"];const isValidNote = (note) => {  chromatic.forEach((item) => {    if (item.split("/").length > 1) {      console.log(item.split("/")[1] == note); // logs true on 3rd iteration      if (item.split("/")[0] == note) return true;      if (item.split("/")[1] == note) return true;    } else if (item == note) {      return true;    }  });  return false;}console.log(isValidNote("C"));

Answer 1

forEach忽略其回调返回的任何值。请改用for循环，以便return返回到 的调用者isValidNote，而不是被 忽略forEach：

const chromatic = ["A", "A#/Bb", "B/Cb", "B#/C", "C#/Db", "D", "D#/Eb", "E", "E#/Fb", "F", "F#/Gb", "G", "G#/Ab" ];

const isValidNote = (note)=> {

    for (const item of chromatic) {

        if(item.split("/").length > 1){

            if(item.split("/")[0] == note) return true;

            if(item.split("/")[1] == note) return true;

        }

        else if(item == note){

            return true;

        }

    }

    return false;

}

console.log(isValidNote("C"));

或者，更简洁地说：

const chromatic = ["A", "A#/Bb", "B/Cb", "B#/C", "C#/Db", "D", "D#/Eb", "E", "E#/Fb", "F", "F#/Gb", "G", "G#/Ab" ];

const isValidNote = (note)=> {

    for (const item of chromatic) {

        const allNotes = item.split("/");

        if (allNotes.includes(note)) {

            return true;

        }

    }

    return false;

}

console.log(isValidNote("C"));

或者与.some：

const chromatic = ["A", "A#/Bb", "B/Cb", "B#/C", "C#/Db", "D", "D#/Eb", "E", "E#/Fb", "F", "F#/Gb", "G", "G#/Ab" ];

const isValidNote = note => chromatic.some(

  item => item.split("/").includes(note)

);

console.log(isValidNote("C"));

Answer 2

从forEach()回调返回只是继续循环，它不会从isValidNote()函数返回。

使用some()而不是forEach(). 如果任何回调返回 true，则它返回 true。

您还可以使用 来简化回调内的条件includes()。

const chromatic = ["A", "A#/Bb", "B/Cb", "B#/C", "C#/Db", "D", "D#/Eb", "E", "E#/Fb", "F", "F#/Gb", "G", "G#/Ab"];

const isValidNote = note => chromatic.some(item => item.split("/").includes(note));

console.log(isValidNote("C"));