JavaScript "If语句“未返回真值

Question

我编写了一个简单的函数，通过遍历数组和比较值来检查所提供的注释是否有效。

代码总是返回false，我不知道为什么？

当我孤立地运行代码item.split("/")[1] == note时，它返回true (注释= "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。使用for循环，这样return将返回到isValidNote的调用方，而不是被forEach忽略

​

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，更简单地说：

​

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"));

​

或使用.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()回调返回只会继续循环，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，则返回true。

您还可以使用includes()简化回调内部的条件。

​

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"));

​