如果你有一个数组值的对象。这里有一个很好的例子。让我们假设您希望根据所拥有的文件的扩展名显示一个图标。具有相同图标的所有扩展都在相同的对象值下。

注意:将这里的case包装在一个对象中要比使用大量case进行切换要好。

检查下面的代码片段(用es6编写)，看看我们如何为特定的扩展返回特定的键。

我从这个git仓库拿到了扩展名列表

// Oject that contains different icons for different extentions const icons = { "music": ["mp3", "m4a", "ogg", "acc", "flac","m3u", "wav"], "video": ["mp4","webm", "mkv", "avi", "mov", "m4v", "mpeg"], "image": ["jpg", "gif", "png", "jpeg", "tif", "psd", "raw", "ico"], "archives": ["zip", "rar", "tar", "dmg", "jar"], "3d-files": ["3ds", "dwg", "obj", "dae", "skp", "fbx"], "text": ["doc", "rtf", "txt", "odt", "tex"], "vector-graphics":["ai", "svg"], "pdf": ["pdf"], "data": ["xml", "csv", "xls"] } const get_icon_Key =( icons_object,file_extention) => { // For each key we chack if the value is contained in the list of values let key = Object.keys(icons_object).find( k=> icons[k].find( // At this leve we check if the extention exist in the array of the specific object value ie. 'music', 'video' ... icons_ext => icons_ext === file_extention) // if we find it means this is the key we are looking for ? true: false); return key } console.log(`The icon of for mp3 extention is: => ${get_icon_Key(icons,"mp3")}`) console.log(`The icon of for mp4 extention is: => ${get_icon_Key(icons,"mp4")}`)

这是Underscorejs方法的一个小扩展，并使用Lodash代替:

var getKeyByValue = function(searchValue) {
  return _.findKey(hash, function(hashValue) {
    return searchValue === hashValue;
  });
}

FindKey将搜索并返回与值匹配的第一个键。 如果你想要最后一个匹配，使用FindLastKey代替。

我使用这个函数:

Object.prototype.getKey = function(value){
  for(var key in this){
    if(this[key] == value){
      return key;
    }
  }
  return null;
};

用法:

// ISO 639: 2-letter codes
var languageCodes = {
  DA: 'Danish',
  DE: 'German',
  DZ: 'Bhutani',
  EL: 'Greek',
  EN: 'English',
  EO: 'Esperanto',
  ES: 'Spanish'
};

var key = languageCodes.getKey('Greek');
console.log(key); // EL

function getKeyByValue(object, value) {
  return Object.keys(object).find(key => object[key] === value);
}

ES6，没有原型突变或外部库。

的例子,

函数getKeyByValue(对象，值){ 返回种(对象)。Find (key =>对象[key] === value); ｝ Const map = {"first": "1"， "second": "2"}; console.log (getKeyByValue(地图,“2”));

给定输入={"a":"x"， "b":"y"， "c":"x"}…

使用第一个值(如输出={“x”:“一”,“y”:“b”}):

输入= { “一个”:“x”, “b”:“y”, “c”:“x” ｝ output = Object.keys(input)。reduceRight(函数(accum, key, i) { Accum [input[key]] = key; 返回accum; }, {}) console.log(输出)

使用最后一个值(例如输出={“x”:“c”、“y”:“b”}):

输入= { “一个”:“x”, “b”:“y”, “c”:“x” ｝ output = Object.keys(input)。Reduce(函数(accum, key, i) { Accum [input[key]] = key; 返回accum; }, {}) console.log(输出)

为每个值数组的键(例如输出={“x”:“c”,“a”,“y”:[b]}):

输入= { “一个”:“x”, “b”:“y”, “c”:“x” ｝ output = Object.keys(input)。reduceRight(函数(accum, key, i) { accum[输入[主要]]= (accum[输入[键 ]] || []). concat(关键); 返回accum; }, {}) console.log(输出)

这里有一个Lodash解决方案，适用于flat key =>值对象，而不是嵌套对象。已接受的答案建议使用_。findKey适用于具有嵌套对象的对象，但在这种常见情况下不起作用。

这种方法将对象颠倒，将键交换为值，然后通过查找新(颠倒的)对象上的值来查找键。如果没有找到键，则返回false，我更喜欢undefined，但你可以很容易地在_的第三个参数中交换它。getKey()中的get方法。

// Get an object's key by value var getKey = function( obj, value ) { var inverse = _.invert( obj ); return _.get( inverse, value, false ); }; // US states used as an example var states = { "AL": "Alabama", "AK": "Alaska", "AS": "American Samoa", "AZ": "Arizona", "AR": "Arkansas", "CA": "California", "CO": "Colorado", "CT": "Connecticut", "DE": "Delaware", "DC": "District Of Columbia", "FM": "Federated States Of Micronesia", "FL": "Florida", "GA": "Georgia", "GU": "Guam", "HI": "Hawaii", "ID": "Idaho", "IL": "Illinois", "IN": "Indiana", "IA": "Iowa", "KS": "Kansas", "KY": "Kentucky", "LA": "Louisiana", "ME": "Maine", "MH": "Marshall Islands", "MD": "Maryland", "MA": "Massachusetts", "MI": "Michigan", "MN": "Minnesota", "MS": "Mississippi", "MO": "Missouri", "MT": "Montana", "NE": "Nebraska", "NV": "Nevada", "NH": "New Hampshire", "NJ": "New Jersey", "NM": "New Mexico", "NY": "New York", "NC": "North Carolina", "ND": "North Dakota", "MP": "Northern Mariana Islands", "OH": "Ohio", "OK": "Oklahoma", "OR": "Oregon", "PW": "Palau", "PA": "Pennsylvania", "PR": "Puerto Rico", "RI": "Rhode Island", "SC": "South Carolina", "SD": "South Dakota", "TN": "Tennessee", "TX": "Texas", "UT": "Utah", "VT": "Vermont", "VI": "Virgin Islands", "VA": "Virginia", "WA": "Washington", "WV": "West Virginia", "WI": "Wisconsin", "WY": "Wyoming" }; console.log( 'The key for "Massachusetts" is "' + getKey( states, 'Massachusetts' ) + '"' ); <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>