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<!doctype html>
<html lang="en">
<head>
<title>JavaScript Patterns</title>
<meta charset="utf-8">
</head>
<body>
<script>
/* Title: Memoization
Description: use function properties to avoid repeated computation
*/
// antipattern
// reason see: https://github.com/shichuan/javascript-patterns/issues/6
var myFunc = function (param) {
if (!myFunc.cache[param]) {
var result = {};
// ... expensive operation ...
myFunc.cache[param] = result;
}
return myFunc.cache[param];
};
// cache storage
myFunc.cache = {};
// preferred method 1
// only one argument using param
var myFunc = function (param) {
if (!myFunc.cache.hasOwnProperty(param)) {
var result = {};
// ... expensive operation ...
myFunc.cache[param] = result;
}
return myFunc.cache[param];
};
// cache storage
myFunc.cache = {};
// preferred method 2
// multiple arguments using JSON stringify
// this will only work correctly for primitive (and Array) arguments,
// since the order in which properties of Objects are enumerated is undetermined
// and can even change between enumerations.
// (a JSON encoder that sorts the keys won't have this issue).
var myFunc = function () {
var cachekey = JSON.stringify(Array.prototype.slice.call(arguments)),
result;
if (!myFunc.cache[cachekey]) {
result = {};
// ... expensive operation ...
myFunc.cache[cachekey] = result;
}
return myFunc.cache[cachekey];
};
// cache storage
myFunc.cache = {};
// preferred method 3
// multiple arguments using arguments.callee
var myFunc = function (param) {
var f = arguments.callee,
result;
if (!f.cache[param]) {
result = {};
// ... expensive operation ...
f.cache[param] = result;
}
return f.cache[param];
};
// cache storage
myFunc.cache = {};
</script>
</body>
</html>