javascript function property

Javascript functions are objects, so they can have properties and methods. Actually, they do. When you create a function, the function has a length property that indicates the number of arguments the function expects. A very simple example:

var getUserById = function(id) {

     var user = {id : id};

     //do other tasks

     return user;

}

//show 1

console.log(getUserById.length);

Another usage of function property is we can cache the result of a function, so we don't have to repeat the same computation again & again.

var calculation = function(seed) {

    if (!calculation.cache[seed]) {

        //do some expensive calculation based on seed

        var result = (seed * seed * 3 + 15) / 3.14;

        calculation.cache[seed] = result;

        console.log('calculation is done for ' + seed);

    }

    return calculation.cache[seed];

};

calculation.cache = {};

//you can see console log 'calculation is done for 3'

var testOne = calculation(3);

//you won't see console log because the result is return directly from cache.

var testTwo = calculation(3);