CODEWITHSUNDEEP
javascript
user3259232
user3259232

Reputation: 95

Explanation of Following Javascript Code

I am fairly new to js and I have been looking at the Mozilla Developer site. Under the functions section, I can't seem to grasp the following

function map(f,a) {
  var result = [], // Create a new Array
      i;
  for (i = 0; i != a.length; i++)
    result[i] = f(a[i]);
  return result;
}

particulary, this line "result[i] = f(a[i]);"

From Mozilla: Function expressions are convenient when passing a function as an argument to another function. The following example shows a map function being defined and then called with an anonymous function as its first parameter

Can you help explain this?

Here is a link for reference. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Functions

Upvotes: -1

Views: 67

Answers (2)

Jeremy Quinton
Jeremy Quinton

Reputation: 686

result[i] = f(a[i]);

result is an array and the element at index i is being assigned the result of a function call which takes the parameter a[i].

f in the line above is an anonymous function which is parsed into the map function as the first argument. f would be defined somewhere else in code with the following syntax

function(value) {
    return result. 
}

The calling code of your example above would look something like.

var array = map(function(value) { return result; },[1,2,3,4,5]);

I would read up on anonymous functions here which might help. http://en.wikibooks.org/wiki/JavaScript/Anonymous_Functions

Upvotes: -1

smnbbrv
smnbbrv

Reputation: 24531

this piece of code applies to every element of array "a" function "f" and returns the array "result" which contains the results of running function "f" for every element in "a".

Sorry, I've got a recursion :)

Actually it can be used like that:

var array = map(function(val){ return val + 1; },[1,2,3,4,5]);

and in "array" you will have these values:

[2,3,4,5,6]

Upvotes: 0

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