Principle
- Make variables shouldn't be changed stand out using all caps.
- Add constants as static properties to the constructor function.
// constructor
var Widget = function () {
// implementation...
};
// constants
Widget.MAX_HEIGHT = 320;
Widget.MAX_WIDTH = 480;
- General-purpose constant object
set(name, value) // To define a new constant
isDefined(name) // To check whether a constant exists
get(name) // To get the value of a constant
var constant = (function () {
var constants = {},
ownProp = Object.prototype.hasOwnProperty,
allowed = {
string: 1,
number: 1,
boolean: 1
},
prefix = (Math.random() + "_").slice(2);
return {
set: function (name, value) {
if (this.isDefined(name)) {
return false;
}
if (!ownProp.call(allowed, typeof value)) {
return false;
}
constants[prefix + name] = value;
return true;
},
isDefined: function (name) {
return ownProp.call(constants, prefix + name);
},
get: function (name) {
if (this.isDefined(name)) {
return constants[prefix + name];
}
return null;
}
};
}());
Testing the implementation：
// check if defined
constant.isDefined("maxwidth"); // false
// define
constant.set("maxwidth", 480); // true
// check again
constant.isDefined("maxwidth"); // true
// attempt to redefine
constant.set("maxwidth", 320); // false
// is the value still intact?
constant.get("maxwidth"); //
References:
JavaScript Patterns - by Stoyan Stefanov (O`Reilly)