javascript master class with Amy Hoy and Thomas Fuchs: Homework part 1

jsmc homework part 2

// Part 1.
// Implement a function prototype extension that caches function results for
// the same input arguments of a function with one parameter.
//
// For example:
// Make sin(1) have the result of Math.sin(1), but use a cached value
// for future calls.
//
// Part 2.
// Use this new function to refactor the code example.
// Some good test numbers: 524287, 9369319, 2147483647 (all primes)

Function.prototype.cached = function( num, method ){
    if( this.cache == null ){
        this.cache = {};
    }
    if( this.cache[ num ] != null ){
        return this.cache[ num ];
    }else{        
        var result = method( num );
        this.cache[ num ] = result + '(cache hit)';
        return result;
    }   
}

function cachedSin( num ) {    
    return cachedSin.cached( num, function( num ){
        // everything but 1 can be prime
        var sin = Math.sin(num);
        return sin;   
    });    
};

function isPrime( num ) {    
    return isPrime.cached( num, function( num ){
        // everything but 1 can be prime
        var prime = num != 1;
        for ( var i = 2; i < num; i++ ) { 
            if ( num % i == 0 ) { 
                prime = false; 
                break; 
            } 
        }
        return prime;   
    });    
};

console.log( isPrime(524287) );
console.log( isPrime(524287) );
console.log( cachedSin(1) );
console.log( cachedSin(1) );