Function properties

Since functions are objects, and objects are mutable in JavaScript, you can add properties to your functions.

Why? For caching results of computations for example. Here's a memoization done this way.

function myFunc(param){
    if (!myFunc.cache) {
        myFunc.cache = {};
    if (!myFunc.cache[param]) {
        var result = {}; // ...
        myFunc.cache[param] = result;
    return myFunc.cache[param];

Here myFunc() gets a cache property which is an object. The function does the complicated computations based on a parameter and ends up with a result object. Using the parameter as a key in the cache object, it stores the result.

Consecutive calls with the same parameter will get the result from the cache, no need to compute the same result again.

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