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"));