How does this for loop condition work?

eloquent, for-loop, javascript, loops

Solution

First we can write the program in a different way it will be more understandable

function listToArray(list) {

  array = [];
  for (var i=list;i; i = i.rest)
  {
    array.push(i.value);
   alert(array)
  }
}

var listobject = { value: 10, rest: { value: 20, rest: { value: 30, rest: null } } };

listToArray(listobject);

Here listobject is an object literal and using the for loop we are traverse through the values of the object literal , or properties of object literal.

We can take each line of the code

1) `listToArray(listobject);`

this is the function call, here we are passing object as an argument to the function.

2)When this code executes then the control goes to the function definition

 function listToArray(list) { ...}

Here the list is the same argument what we are passing at the time of function call.

3) `array = [];` inside the function we are declaring an array, initially the array has no elements.

4)next is our for loop. `for (var i=list;list; i = i.rest)`

inside loop first we assigning var i=list;

means we are assign all the property of the object list to i

That means we can access every property of object via `i`,

example:

i.value will result 10

5) next Condition statement here it is `i` and in your program it is node

all have same meaning in this case :

the condition will false when `i` is null, in your case `node` is null.

6)`i=i.rest`

it will give the property of the object or value of the object.

Example : `listobject.value will result 10`

listobject.rest.value will result 20

listobject.rest.rest.value will result 30

7) and finally `array.push(i.value);`

add the values to our array and in this our array contains 10,20,30

Problem

Original source