fromCharCode() 可接受一个指定的 Unicode 值，然后返回一个字符串。

常用数字、字母对应Unicode 的值

for(var i=48;i<=57;i++){
    document.write(String.fromCharCode(i))  //0123456789
}


for(var i=65;i<=90;i++){
    document.write(String.fromCharCode(i)) //ABCDEFGHIJKLMNOPQRSTUVWXYZ
}


for(var i=97;i<=122;i++){
    document.write(String.fromCharCode(i)) //abcdefghijklmnopqrstuvwxyz
}

用于

用于为接口返回的城市列表排序

接口返回的城市列表数据是这样的

{
    "E": [
        {
            "name": "鄂州",
            "id": 184
        },
        {
            "name": "峨眉山",
            "id": 213
        }
    ],
    "A": [
        {
            "name": "安庆",
            "id": 70
        },
        {
            "name": "鞍山",
            "id": 96
        }
    ],
    "R": [
        {
            "name": "日照",
            "id": 58
        }
    ],
    "M": [
        {
            "name": "玛沁县",
            "id": 2382
        },
        {
            "name": "玛多县",
            "id": 2387
        }
    ]
}

用以下方法把数据从A-Z排序

function sortAllCities(allCities){
  let newObj = {};
  for(let i=65;i<=90;i++){
    if(allCities[String.fromCharCode(i)]){
      newObj[String.fromCharCode(i)] = allCities[String.fromCharCode(i)];
    }
  }
  return newObj;
}

排序后数据是这样的

{
    "A": [
        {
            "name": "安庆",
            "id": 70
        },
        {
            "name": "鞍山",
            "id": 96
        }
    ],
    "E": [
        {
            "name": "鄂州",
            "id": 184
        },
        {
            "name": "峨眉山",
            "id": 213
        }
    ],
    "M": [
        {
            "name": "玛沁县",
            "id": 2382
        },
        {
            "name": "玛多县",
            "id": 2387
        }
    ],
    "R": [
        {
            "name": "日照",
            "id": 58
        }
    ]
}