JavaScript for…in vs for

Question

Do you think there is a big difference in for...in and for loops? What kind of \"for\" do you prefer to use and why?

Let\'s say we have an array of associative array

Answer 1

Although they both are very much alike there is a minor difference :

var array = ["a", "b", "c"];
array["abc"] = 123;
console.log("Standard for loop:");
for (var index = 0; index < array.length; index++)
{
  console.log(" array[" + index + "] = " + array[index]); //Standard for loop
}

in this case the output is :

STANDARD FOR LOOP:

ARRAY[0] = A

ARRAY[1] = B

ARRAY[2] = C

console.log("For-in loop:");
for (var key in array)
{
  console.log(" array[" + key + "] = " + array[key]); //For-in loop output
}

while in this case the output is:

FOR-IN LOOP:

ARRAY[1] = B

ARRAY[2] = C

ARRAY[10] = D

ARRAY[ABC] = 123