我有一个非常简单的JavaScript对象,我将其用作关联数组。是否有一个简单的函数允许我获取值的键,或者我必须迭代对象并手动找到它?
当前回答
我知道我迟到了,但是你觉得我今天做的这个EMCMAScript 2017解决方案怎么样?它处理多个匹配,因为如果两个键有相同的值会发生什么?这就是我创建这个小片段的原因。
当有一个匹配时,它只返回一个字符串,但当有几个匹配时,它返回一个数组。
let object = { nine_eleven_was_a_inside_job: false, javascript_isnt_useful: false } // Complex, dirty but useful. Handle mutiple matchs which is the main difficulty. Object.prototype.getKeyByValue = function (val) { let array = []; let array2 = []; // Get all the key in the object. for(const [key] of Object.entries(this)) { if (this[key] == val) { // Putting them in the 1st array. array.push(key) } } // List all the value of the 1st array. for(key of array) { // "If one of the key in the array is equal to the value passed in the function (val), it means that 'val' correspond to it." if(this[key] == val) { // Push all the matchs. array2.push(key); } } // Check the lenght of the array. if (array2.length < 2) { // If it's under 2, only return the single value but not in the array. return array2[0]; } else { // If it's above or equal to 2, return the entire array. return array2; } } /* Basic way to do it wich doesn't handle multiple matchs. let getKeyByValue = function (object, val) { for(const [key, content] of Object.entries(object)) { if (object[key] === val) { return key } } } */ console.log(object.getKeyByValue(false))
其他回答
没有可用的标准方法。你需要迭代,你可以创建一个简单的helper:
Object.prototype.getKeyByValue = function( value ) {
for( var prop in this ) {
if( this.hasOwnProperty( prop ) ) {
if( this[ prop ] === value )
return prop;
}
}
}
var test = {
key1: 42,
key2: 'foo'
};
test.getKeyByValue( 42 ); // returns 'key1'
提醒一句:即使上述方法有效,扩展任何主机或本机对象的.prototype通常也不是一个好主意。我这样做是因为它很适合这个问题。不管怎样,你应该在.prototype之外使用这个函数,并将对象传递给它。
如果你正在使用下划线或Lodash库,你可以使用_。findKey功能:
var users = {
'barney': { 'age': 36, 'active': true },
'fred': { 'age': 40, 'active': false },
'pebbles': { 'age': 1, 'active': true }
};
_.findKey(users, function(o) { return o.age < 40; });
// => 'barney' (iteration order is not guaranteed)
// The `_.matches` iteratee shorthand.
_.findKey(users, { 'age': 1, 'active': true });
// => 'pebbles'
// The `_.matchesProperty` iteratee shorthand.
_.findKey(users, ['active', false]);
// => 'fred'
// The `_.property` iteratee shorthand.
_.findKey(users, 'active');
// => 'barney'
真的很简单。
const CryptoEnum = Object.freeze({
"Bitcoin": 0, "Ethereum": 1,
"Filecoin": 2, "Monero": 3,
"EOS": 4, "Cardano": 5,
"NEO": 6, "Dash": 7,
"Zcash": 8, "Decred": 9
});
Object.entries(CryptoEnum)[0][0]
// output => "Bitcoin"
ES6方法:
Object.fromEntries(Object.entries(a).map(b => b.reverse()))['value_you_look_for']
我知道我迟到了,但是你觉得我今天做的这个EMCMAScript 2017解决方案怎么样?它处理多个匹配,因为如果两个键有相同的值会发生什么?这就是我创建这个小片段的原因。
当有一个匹配时,它只返回一个字符串,但当有几个匹配时,它返回一个数组。
let object = { nine_eleven_was_a_inside_job: false, javascript_isnt_useful: false } // Complex, dirty but useful. Handle mutiple matchs which is the main difficulty. Object.prototype.getKeyByValue = function (val) { let array = []; let array2 = []; // Get all the key in the object. for(const [key] of Object.entries(this)) { if (this[key] == val) { // Putting them in the 1st array. array.push(key) } } // List all the value of the 1st array. for(key of array) { // "If one of the key in the array is equal to the value passed in the function (val), it means that 'val' correspond to it." if(this[key] == val) { // Push all the matchs. array2.push(key); } } // Check the lenght of the array. if (array2.length < 2) { // If it's under 2, only return the single value but not in the array. return array2[0]; } else { // If it's above or equal to 2, return the entire array. return array2; } } /* Basic way to do it wich doesn't handle multiple matchs. let getKeyByValue = function (object, val) { for(const [key, content] of Object.entries(object)) { if (object[key] === val) { return key } } } */ console.log(object.getKeyByValue(false))