在这个答案的更新3中已经明确表示，这个符号:
var hash = {};
hash[X]
实际上并不散列对象X;它实际上只是将X转换为一个字符串(如果它是一个对象，则通过. tostring()，或者其他一些用于各种基本类型的内置转换)，然后在“哈希”中查找该字符串，而不散列它。对象相等性也不检查-如果两个不同的对象具有相同的字符串转换，它们将相互覆盖。
鉴于此，JavaScript中是否有有效的hashmap实现?
(例如，javascript hashmap的第二个谷歌结果对任何操作产生的实现都是O(n)。其他各种结果忽略了具有等效字符串表示的不同对象会相互覆盖这一事实。
当前回答
根据ECMAScript 2015 (ES6)，标准JavaScript有一个Map实现。更多信息可以在这里找到。
基本用法:
var myMap = new Map();
var keyString = "a string",
keyObj = {},
keyFunc = function () {};
// Setting the values
myMap.set(keyString, "value associated with 'a string'");
myMap.set(keyObj, "value associated with keyObj");
myMap.set(keyFunc, "value associated with keyFunc");
myMap.size; // 3
// Getting the values
myMap.get(keyString); // "value associated with 'a string'"
myMap.get(keyObj); // "value associated with keyObj"
myMap.get(keyFunc); // "value associated with keyFunc"
其他回答
试试我的JavaScript哈希表实现:http://www.timdown.co.uk/jshashtable
它查找关键对象的hashCode()方法，或者您可以在创建Hashtable对象时提供哈希函数。
我的“地图”实现，源自Christoph的例子:
使用示例:
var map = new Map(); // Creates an "in-memory" map
var map = new Map("storageId"); // Creates a map that is loaded/persisted using html5 storage
function Map(storageId) {
this.current = undefined;
this.size = 0;
this.storageId = storageId;
if (this.storageId) {
this.keys = new Array();
this.disableLinking();
}
}
Map.noop = function() {
return this;
};
Map.illegal = function() {
throw new Error("illegal operation for maps without linking");
};
// Map initialisation from an existing object
// doesn't add inherited properties if not explicitly instructed to:
// omitting foreignKeys means foreignKeys === undefined, i.e. == false
// --> inherited properties won't be added
Map.from = function(obj, foreignKeys) {
var map = new Map;
for(var prop in obj) {
if(foreignKeys || obj.hasOwnProperty(prop))
map.put(prop, obj[prop]);
}
return map;
};
Map.prototype.disableLinking = function() {
this.link = Map.noop;
this.unlink = Map.noop;
this.disableLinking = Map.noop;
this.next = Map.illegal;
this.key = Map.illegal;
this.value = Map.illegal;
// this.removeAll = Map.illegal;
return this;
};
// Overwrite in Map instance if necessary
Map.prototype.hash = function(value) {
return (typeof value) + ' ' + (value instanceof Object ?
(value.__hash || (value.__hash = ++arguments.callee.current)) :
value.toString());
};
Map.prototype.hash.current = 0;
// --- Mapping functions
Map.prototype.get = function(key) {
var item = this[this.hash(key)];
if (item === undefined) {
if (this.storageId) {
try {
var itemStr = localStorage.getItem(this.storageId + key);
if (itemStr && itemStr !== 'undefined') {
item = JSON.parse(itemStr);
this[this.hash(key)] = item;
this.keys.push(key);
++this.size;
}
} catch (e) {
console.log(e);
}
}
}
return item === undefined ? undefined : item.value;
};
Map.prototype.put = function(key, value) {
var hash = this.hash(key);
if(this[hash] === undefined) {
var item = { key : key, value : value };
this[hash] = item;
this.link(item);
++this.size;
}
else this[hash].value = value;
if (this.storageId) {
this.keys.push(key);
try {
localStorage.setItem(this.storageId + key, JSON.stringify(this[hash]));
} catch (e) {
console.log(e);
}
}
return this;
};
Map.prototype.remove = function(key) {
var hash = this.hash(key);
var item = this[hash];
if(item !== undefined) {
--this.size;
this.unlink(item);
delete this[hash];
}
if (this.storageId) {
try {
localStorage.setItem(this.storageId + key, undefined);
} catch (e) {
console.log(e);
}
}
return this;
};
// Only works if linked
Map.prototype.removeAll = function() {
if (this.storageId) {
for (var i=0; i<this.keys.length; i++) {
this.remove(this.keys[i]);
}
this.keys.length = 0;
} else {
while(this.size)
this.remove(this.key());
}
return this;
};
// --- Linked list helper functions
Map.prototype.link = function(item) {
if (this.storageId) {
return;
}
if(this.size == 0) {
item.prev = item;
item.next = item;
this.current = item;
}
else {
item.prev = this.current.prev;
item.prev.next = item;
item.next = this.current;
this.current.prev = item;
}
};
Map.prototype.unlink = function(item) {
if (this.storageId) {
return;
}
if(this.size == 0)
this.current = undefined;
else {
item.prev.next = item.next;
item.next.prev = item.prev;
if(item === this.current)
this.current = item.next;
}
};
// --- Iterator functions - only work if map is linked
Map.prototype.next = function() {
this.current = this.current.next;
};
Map.prototype.key = function() {
if (this.storageId) {
return undefined;
} else {
return this.current.key;
}
};
Map.prototype.value = function() {
if (this.storageId) {
return undefined;
}
return this.current.value;
};
这看起来很健壮 解决方案:https://github.com/flesler/hashmap
它甚至可以很好地用于看起来相同的函数和对象。它使用的唯一hack是向对象添加一个模糊成员来标识它。如果您的程序没有覆盖这个模糊的变量(它类似于hashid)，那么您就很好了。
根据ECMAScript 2015 (ES6)，标准JavaScript有一个Map实现。更多信息可以在这里找到。
基本用法:
var myMap = new Map();
var keyString = "a string",
keyObj = {},
keyFunc = function () {};
// Setting the values
myMap.set(keyString, "value associated with 'a string'");
myMap.set(keyObj, "value associated with keyObj");
myMap.set(keyFunc, "value associated with keyFunc");
myMap.size; // 3
// Getting the values
myMap.get(keyString); // "value associated with 'a string'"
myMap.get(keyObj); // "value associated with keyObj"
myMap.get(keyFunc); // "value associated with keyFunc"
不幸的是，之前的答案都不适合我的情况:不同的键对象可能具有相同的散列代码。因此，我写了一个简单的类似java的HashMap版本:
function HashMap() {
this.buckets = {};
}
HashMap.prototype.put = function(key, value) {
var hashCode = key.hashCode();
var bucket = this.buckets[hashCode];
if (!bucket) {
bucket = new Array();
this.buckets[hashCode] = bucket;
}
for (var i = 0; i < bucket.length; ++i) {
if (bucket[i].key.equals(key)) {
bucket[i].value = value;
return;
}
}
bucket.push({ key: key, value: value });
}
HashMap.prototype.get = function(key) {
var hashCode = key.hashCode();
var bucket = this.buckets[hashCode];
if (!bucket) {
return null;
}
for (var i = 0; i < bucket.length; ++i) {
if (bucket[i].key.equals(key)) {
return bucket[i].value;
}
}
}
HashMap.prototype.keys = function() {
var keys = new Array();
for (var hashKey in this.buckets) {
var bucket = this.buckets[hashKey];
for (var i = 0; i < bucket.length; ++i) {
keys.push(bucket[i].key);
}
}
return keys;
}
HashMap.prototype.values = function() {
var values = new Array();
for (var hashKey in this.buckets) {
var bucket = this.buckets[hashKey];
for (var i = 0; i < bucket.length; ++i) {
values.push(bucket[i].value);
}
}
return values;
}
注意:键对象必须“实现”hashCode()和equals()方法。
