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@wmhilton
Last active Dec 18, 2015
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Dict Object for JavaScript
/*
* Dict Object for JavaScript (https://gist.github.com/wmhilton/5859079)
* Author: William Hilton (wmhilton@gmail.com)
* License: http://opensource.org/licenses/MIT
*
* Say you want something like a Python "dictionary" or a Java "map" where you
* are storing (String key, Object value) pairs. It's tempting to do it using
* object properties in JavaScript, since
* obj['key'] = value
* works so conveniently. However, say you want to be able to have some properties
* on your dictionary like compute its size, or have methods like sort(), or have
* assignable attributes like .name. Since you are already using the object's
* properties as your (key,value) map adding these features is a little tricky.
* Here's an example of how to accomplish such a thing.
*/
var Dict = function() {};
Dict.prototype = {
// A read-only property to compute the size of the dictionary.
get count() {
return Object.keys(this).length;
},
// Here is a custom property that can be set and get.
get expectedCount() {
return _expCnt;
},
set expectedCount(val) {
_expCnt = val;
},
// This allows us to iterate easily over the members using .forEach()
asArray: function() {
var arr = [];
for (var prop in this) {
if (this.hasOwnProperty(prop)) {
arr.push(this[prop]);
}
}
return arr;
}
};
// By defining this property, we can store the value "tucked away" inside the prototype.
Dict.prototype._expCnt = 0;
/*
foo = new Dict()
// Dict {}
// Notice how in the debugger, foo appears to have no properties.
// Both the count and expectedCount are not properties of foo, but of foo's prototype.
foo.count
// 0
foo['bar'] = 'jawn';
foo.count
// 1
foo['sam'] = 1;
foo.bob = 1;
// Just demonstrating both ways of setting a Javascript object property.
foo.count
// 3
foo.expectedCount
// 0
foo.expectedCount = 3;
// Note that .count doesn't increase
foo.count
// 3
foo.expectedCount
// 3
// We have successfully stored a piece of data in foo, without
// adding a property to the foo object and messing up our (key,value) map.
*/
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