I need to store some statistics using JavaScript in a way like I'd do it in C#:
Dictionary<string, int> statistics; statistics["Foo"] = 10; statistics["Goo"] = statistics["Goo"] + 1; statistics.Add("Zoo", 1); Is there an Hashtable or something like Dictionary<TKey, TValue> in JavaScript? How could I store values in such a way?
Use JavaScript objects as associative arrays.
Associative Array: In simple words associative arrays use Strings instead of Integer numbers as index.
Create an object with
var dictionary = {}; JavaScript allows you to add properties to objects by using the following syntax:
Object.yourProperty = value; An alternate syntax for the same is:
Object["yourProperty"] = value; If you can, also create key-to-value object maps with the following syntax:
var point = { x:3, y:2 }; point["x"] // returns 3 point.y // returns 2 You can iterate through an associative array using the for..in loop construct as follows
for(var key in Object.keys(dict)){ var value = dict[key]; /* use key/value for intended purpose */ } 
new Array() is frowned up. The article eventually mentions its drawbacks and suggests new Object() or {} as preferred alternatives, but that's near the end and I fear most readers won't get that far.CommentedMay 16, 2015 at 5:55var obj1 = {}; var obj2 = {}; var table= {}; table[obj1] = "A"; table[obj2] = "B"; alert(table[obj1]); //displays B, because it can't differentiate between keys obj1 and obj2; they're both converted to string and just become something like "Object". Total fail, and makes type-safe serialization with references and cyclic-references intact difficult or non-performant in JavaScript. It's easy in Flash/AS3.Point.prototype.equals = function(obj) { return (obj instanceof Point) && (obj.x === this.x) && (obj.y === this.y); };for... in for a dictionary will loop over its keys, so Object.keys seems malplaced there. Object.keys returns an array of the keys of the dictionary, and for... in for an array loops over its "keys", which for an array are its indices, not its values.var associativeArray = {}; associativeArray["one"] = "First"; associativeArray["two"] = "Second"; associativeArray["three"] = "Third"; If you are coming from an object-oriented language you should check this article.
All modern browsers support a JavaScript Map object. There are a couple of reasons that make using a Map better than using an object:
Map.Map easily while you have to keep track of the size for an object.Example:
var myMap = new Map(); var keyObj = {}, keyFunc = function () {}, keyString = "a string"; myMap.set(keyString, "value associated with 'a string'"); myMap.set(keyObj, "value associated with keyObj"); myMap.set(keyFunc, "value associated with keyFunc"); console.log(myMap.size); // 3 console.log(myMap.get(keyString)); // "value associated with 'a string'" console.log(myMap.get(keyObj)); // "value associated with keyObj" console.log(myMap.get(keyFunc)); // "value associated with keyFunc"If you want keys that are not referenced from other objects to be garbage collected, consider using a WeakMap instead of a Map.
Map is barely useful when your key is an object but should be compared by value, not reference.CommentedDec 11, 2015 at 15:07Unless you have a specific reason not to, just use a normal object. Object properties in JavaScript can be referenced using hashtable-style syntax:
var hashtable = {}; hashtable.foo = "bar"; hashtable['bar'] = "foo"; Both foo and bar elements can now then be referenced as:
hashtable['foo']; hashtable['bar']; // Or hashtable.foo; hashtable.bar; Of course this does mean your keys have to be strings. If they're not strings they are converted internally to strings, so it may still work. Your mileage may vary.
var hash = {}; hash[1] = "foo"; alert(hash["1"]); alerts "foo".var dict = {}; dict.key1 = "val1"; dict["key2"] = "val2"; dict's key1 element can be referenced equivalently by both dict["key1"] and dict.key1.Since every object in JavaScript behaves like - and is generally implemented as - a hashtable, I just go with that...
var hashSweetHashTable = {}; 
if (hashSweetHashTable.foo) should enter the if block if foo is set.CommentedAug 30, 2019 at 1:01In C# the code looks like:
Dictionary<string,int> dictionary = new Dictionary<string,int>(); dictionary.add("sample1", 1); dictionary.add("sample2", 2); or
var dictionary = new Dictionary<string, int> { {"sample1", 1}, {"sample2", 2} }; In JavaScript:
var dictionary = { "sample1": 1, "sample2": 2 } A C# dictionary object contains useful methods, like dictionary.ContainsKey()
In JavaScript, we could use the hasOwnProperty like:
if (dictionary.hasOwnProperty("sample1")) console.log("sample1 key found and its value is"+ dictionary["sample1"]); If you require your keys to be any object rather than just strings, then you could use my jshashtable.
Several years ago, I had implemented the following hashtable, which has had some features that were missing to the Map class. However, that's no longer the case — now, it's possible to iterate over the entries of a Map, get an array of its keys or values or both (these operations are implemented copying to a newly allocated array, though — that's a waste of memory and its time complexity will always be as slow as O(n)), remove specific items given their key, and clear the whole map.
Therefore, my hashtable implementation is only useful for compatibility purposes, in which case it'd be a saner approach to write a proper polyfill based on this.
function Hashtable() { this._map = new Map(); this._indexes = new Map(); this._keys = []; this._values = []; this.put = function(key, value) { var newKey = !this.containsKey(key); this._map.set(key, value); if (newKey) { this._indexes.set(key, this.length); this._keys.push(key); this._values.push(value); } }; this.remove = function(key) { if (!this.containsKey(key)) return; this._map.delete(key); var index = this._indexes.get(key); this._indexes.delete(key); this._keys.splice(index, 1); this._values.splice(index, 1); }; this.indexOfKey = function(key) { return this._indexes.get(key); }; this.indexOfValue = function(value) { return this._values.indexOf(value) != -1; }; this.get = function(key) { return this._map.get(key); }; this.entryAt = function(index) { var item = {}; Object.defineProperty(item, "key", { value: this.keys[index], writable: false }); Object.defineProperty(item, "value", { value: this.values[index], writable: false }); return item; }; this.clear = function() { var length = this.length; for (var i = 0; i < length; i++) { var key = this.keys[i]; this._map.delete(key); this._indexes.delete(key); } this._keys.splice(0, length); }; this.containsKey = function(key) { return this._map.has(key); }; this.containsValue = function(value) { return this._values.indexOf(value) != -1; }; this.forEach = function(iterator) { for (var i = 0; i < this.length; i++) iterator(this.keys[i], this.values[i], i); }; Object.defineProperty(this, "length", { get: function() { return this._keys.length; } }); Object.defineProperty(this, "keys", { get: function() { return this._keys; } }); Object.defineProperty(this, "values", { get: function() { return this._values; } }); Object.defineProperty(this, "entries", { get: function() { var entries = new Array(this.length); for (var i = 0; i < entries.length; i++) entries[i] = this.entryAt(i); return entries; } }); } Hashtableget(key)Returns the value associated to the specified key.
Parameters:key: The key from which to retrieve the value.
put(key, value)Associates the specified value to the specified key.
Parameters:key: The key to which associate the value.value: The value to associate to the key.
remove(key)Removes the specified key, together with the value associated to it.
Parameters:key: The key to remove.
clear()Clears the whole hashtable, by removing all its entries.
indexOfKey(key)Returns the index of the specified key, according to the order entries have been added.
Parameters:key: The key of which to get the index.
indexOfValue(value)Returns the index of the specified value, according to the order entries have been added.
Parameters:value: The value of which to get the index.
Remarks:
Values are compared by identity.
entryAt(index)Returns an object with a key and a value properties, representing the entry at the specified index.
Parameters:index: The index of the entry to get.
containsKey(key)Returns whether the hashtable contains the specified key.
Parameters:key: The key to look for.
containsValue(value)Returns whether the hashtable contains the specified value.
Parameters:value: The value to look for.
forEach(iterator)Iterates through all the entries in the hashtable, calling specified iterator.
Parameters:iterator: A method with three parameters, key, value and index, where index represents the index of the entry according to the order it's been added.
length (Read-only)Gets the count of the entries in the hashtable.
keys (Read-only)Gets an array of all the keys in the hashtable.
values (Read-only)Gets an array of all the values in the hashtable.
entries (Read-only)Gets an array of all the entries in the hashtable. They're represented the same as the method entryAt().
function HashTable() { this.length = 0; this.items = new Array(); for (var i = 0; i < arguments.length; i += 2) { if (typeof (arguments[i + 1]) != 'undefined') { this.items[arguments[i]] = arguments[i + 1]; this.length++; } } this.removeItem = function (in_key) { var tmp_previous; if (typeof (this.items[in_key]) != 'undefined') { this.length--; var tmp_previous = this.items[in_key]; delete this.items[in_key]; } return tmp_previous; } this.getItem = function (in_key) { return this.items[in_key]; } this.setItem = function (in_key, in_value) { var tmp_previous; if (typeof (in_value) != 'undefined') { if (typeof (this.items[in_key]) == 'undefined') { this.length++; } else { tmp_previous = this.items[in_key]; } this.items[in_key] = in_value; } return tmp_previous; } this.hasItem = function (in_key) { return typeof (this.items[in_key]) != 'undefined'; } this.clear = function () { for (var i in this.items) { delete this.items[i]; } this.length = 0; } } 
{} not an array: [] or new Array() if you intend to have string keys otherwise the js engine has a problem -- it will either see 2 types for 1 variable which means no optimization or it will run with array and realize it has to change to object (possible re-allocation).CommentedSep 4, 2015 at 20:13https://gist.github.com/alexhawkins/f6329420f40e5cafa0a4
var HashTable = function() { this._storage = []; this._count = 0; this._limit = 8; } HashTable.prototype.insert = function(key, value) { // Create an index for our storage location by passing // it through our hashing function var index = this.hashFunc(key, this._limit); // Retrieve the bucket at this particular index in // our storage, if one exists //[[ [k,v], [k,v], [k,v] ] , [ [k,v], [k,v] ] [ [k,v] ] ] var bucket = this._storage[index] // Does a bucket exist or do we get undefined // when trying to retrieve said index? if (!bucket) { // Create the bucket var bucket = []; // Insert the bucket into our hashTable this._storage[index] = bucket; } var override = false; // Now iterate through our bucket to see if there are any conflicting // key value pairs within our bucket. If there are any, override them. for (var i = 0; i < bucket.length; i++) { var tuple = bucket[i]; if (tuple[0] === key) { // Override value stored at this key tuple[1] = value; override = true; } } if (!override) { // Create a new tuple in our bucket. // Note that this could either be the new empty bucket we created above // or a bucket with other tupules with keys that are different than // the key of the tuple we are inserting. These tupules are in the same // bucket because their keys all equate to the same numeric index when // passing through our hash function. bucket.push([key, value]); this._count++ // Now that we've added our new key/val pair to our storage // let's check to see if we need to resize our storage if (this._count > this._limit * 0.75) { this.resize(this._limit * 2); } } return this; }; HashTable.prototype.remove = function(key) { var index = this.hashFunc(key, this._limit); var bucket = this._storage[index]; if (!bucket) { return null; } // Iterate over the bucket for (var i = 0; i < bucket.length; i++) { var tuple = bucket[i]; // Check to see if key is inside bucket if (tuple[0] === key) { // If it is, get rid of this tuple bucket.splice(i, 1); this._count--; if (this._count < this._limit * 0.25) { this._resize(this._limit / 2); } return tuple[1]; } } }; HashTable.prototype.retrieve = function(key) { var index = this.hashFunc(key, this._limit); var bucket = this._storage[index]; if (!bucket) { return null; } for (var i = 0; i < bucket.length; i++) { var tuple = bucket[i]; if (tuple[0] === key) { return tuple[1]; } } return null; }; HashTable.prototype.hashFunc = function(str, max) { var hash = 0; for (var i = 0; i < str.length; i++) { var letter = str[i]; hash = (hash << 5) + letter.charCodeAt(0); hash = (hash & hash) % max; } return hash; }; HashTable.prototype.resize = function(newLimit) { var oldStorage = this._storage; this._limit = newLimit; this._count = 0; this._storage = []; oldStorage.forEach(function(bucket) { if (!bucket) { return; } for (var i = 0; i < bucket.length; i++) { var tuple = bucket[i]; this.insert(tuple[0], tuple[1]); } }.bind(this)); }; HashTable.prototype.retrieveAll = function() { console.log(this._storage); //console.log(this._limit); }; /******************************TESTS*******************************/ var hashT = new HashTable(); hashT.insert('Alex Hawkins', '510-599-1930'); //hashT.retrieve(); //[ , , , [ [ 'Alex Hawkins', '510-599-1930' ] ] ] hashT.insert('Boo Radley', '520-589-1970'); //hashT.retrieve(); //[ , [ [ 'Boo Radley', '520-589-1970' ] ], , [ [ 'Alex Hawkins', '510-599-1930' ] ] ] hashT.insert('Vance Carter', '120-589-1970').insert('Rick Mires', '520-589-1970').insert('Tom Bradey', '520-589-1970').insert('Biff Tanin', '520-589-1970'); //hashT.retrieveAll(); /* [ , [ [ 'Boo Radley', '520-589-1970' ], [ 'Tom Bradey', '520-589-1970' ] ], , [ [ 'Alex Hawkins', '510-599-1930' ], [ 'Rick Mires', '520-589-1970' ] ], , , [ [ 'Biff Tanin', '520-589-1970' ] ] ] */ // Override example (Phone Number Change) // hashT.insert('Rick Mires', '650-589-1970').insert('Tom Bradey', '818-589-1970').insert('Biff Tanin', '987-589-1970'); //hashT.retrieveAll(); /* [ , [ [ 'Boo Radley', '520-589-1970' ], [ 'Tom Bradey', '818-589-1970' ] ], , [ [ 'Alex Hawkins', '510-599-1930' ], [ 'Rick Mires', '650-589-1970' ] ], , , [ [ 'Biff Tanin', '987-589-1970' ] ] ] */ hashT.remove('Rick Mires'); hashT.remove('Tom Bradey'); //hashT.retrieveAll(); /* [ , [ [ 'Boo Radley', '520-589-1970' ] ], , [ [ 'Alex Hawkins', '510-599-1930' ] ], , , [ [ 'Biff Tanin', '987-589-1970' ] ] ] */ hashT.insert('Dick Mires', '650-589-1970').insert('Lam James', '818-589-1970').insert('Ricky Ticky Tavi', '987-589-1970'); hashT.retrieveAll(); /* NOTICE HOW THE HASH TABLE HAS NOW DOUBLED IN SIZE UPON REACHING 75% CAPACITY, i.e. 6/8. It is now size 16. [, , [ [ 'Vance Carter', '120-589-1970' ] ], [ [ 'Alex Hawkins', '510-599-1930' ], [ 'Dick Mires', '650-589-1970' ], [ 'Lam James', '818-589-1970' ] ], , , , , , [ [ 'Boo Radley', '520-589-1970' ], [ 'Ricky Ticky Tavi', '987-589-1970' ] ], , , , , [ [ 'Biff Tanin', '987-589-1970' ] ] ] */ console.log(hashT.retrieve('Lam James')); // 818-589-1970 console.log(hashT.retrieve('Dick Mires')); // 650-589-1970 console.log(hashT.retrieve('Ricky Ticky Tavi')); //987-589-1970 console.log(hashT.retrieve('Alex Hawkins')); // 510-599-1930 console.log(hashT.retrieve('Lebron James')); // null You can create one using like the following:
var dictionary = { Name:"Some Programmer", Age:24, Job:"Writing Programs" }; // Iterate over using keys for (var key in dictionary) { console.log("Key: " + key + " , " + "Value: "+ dictionary[key]); } // Access a key using object notation: console.log("Her name is: " + dictionary.Name)
