Facing issues writing a JavaScript memoization function

Question

I am trying to write a memoization function, but keep getting the following error.

Error - "TypeError: getNthFibonacciNo is not a function
    at dabebimaya.js:28:38
    at https://static.jsbin.com/js/prod/runner-4.1.4.min.js:1:13924
    at https://static.jsbin.com/js/prod/runner-4.1.4.min.js:1:10866"

How can I find this error in my code? I have tried googling the error with no avail. Please point out any additional errors too if possible.

function memoize(fn) {
  var cache = {};
  if (cache[arguments[0]]!==undefined) {
    return cache[arguments[0]];
  }  
  else {
    var value = fn.apply(this, arguments);
    cache[arguments[0]] = value;  
    return value;
  }
}

var getNthFibonacciNo = memoize(function(n){
    //1,1,2,3,5,8,13,21,34
    if(i<=2)
      return 1;

    var fib = [0,1,1];
    for(var i=3;i<=n;i++) {
      fib[i] = fib[i-2]+fib[i-1];
    }

    return fib[n];
});

console.log(getNthFibonacciNo(7));

intentionally-left-nil · Accepted Answer · 2018-04-14 03:03:13Z

3

Your memoize function isn't returning a function.

function memoize(fn) {
  var cache = {};
  return function() {
    if (cache[arguments[0]]!==undefined) {
      return cache[arguments[0]];
    }  
    else {
      var value = fn.apply(this, arguments);
      cache[arguments[0]] = value;  
      return value;
    }
  }
}

now returns a function so that it can be called multiple times.

Usage

function test(a) {
  console.log('calling test', a);
  return a + 1;
}

const memoized = memoize(test);

memoized(1); // prints calling test and returns 2
memoized(1); // returns 2
memoized(2); // prints calling test and returns 3

edited Apr 14, 2018 at 3:03

answered Apr 14, 2018 at 2:56

intentionally-left-nil

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4 Comments

ibrahim mahrir Over a year ago

You may also consider changing cache[arguments[0]]!==undefined test to a more sophisticated one like: cache.hasOwnProperty(argument[0]).

user2156888 Over a year ago

I keep getting this error when using online js compilers, chrome console. Can you please help?: Uncaught TypeError: fn.apply is not a function at memoize (<anonymous>:8:20) at <anonymous>:27:13

intentionally-left-nil Over a year ago

@user2156888 that error is saying that whatever you are passing into memoize is not a function.

user2156888 Over a year ago

Thanks Anil, looks like I missed return function() { } that you had mentioned earlier. Thanks for the explanation!.

user2156888 · Accepted Answer · 2018-04-16 09:18:33Z

0

I managed to fix my code after suggestions by AnilRedshift. Below is the fixed code.

function memoize(fn) {
  var cache = {};
  return function() {
    var key = JSON.stringify(arguments);
    if (cache[key]) {
      console.log('cache used');
      return cache[key];
    }  
    else {
      var value = fn.apply(this, arguments);
      cache[key] = value;
      console.log('cache not used');
      return value;
    }
  };  
}

var fibonacciMemoized = memoize(function(n) {
    //1,1,2,3,5,8,13,21,34
    if(i<=2)
      return 1;

    var fib = [0,1,1];
    for(var i=3;i<=n;i++) {
      fib[i] = fibonacciMemoized(i-2)+fibonacciMemoized(i-1);
    }

    return fib[n];
});

console.log(fibonacciMemoized(7));

console.log(fibonacciMemoized(9));

edited Apr 16, 2018 at 9:18

answered Apr 16, 2018 at 9:12

user2156888

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