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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Iterating through an Array

Posted by anuj maheshwari
anuj maheshwari
1,314 Points

what's wrong in my code

var inStock = [ 'apples', 'eggs', 'milk', 'cookies', 'cheese', 'bread', 'lettuce', 'carrot', 'broccoli', 'pizza', 'potato', 'crackers', 'onion', 'tofu', 'frozen dinner', 'cucumber'];

for(var i=0; i<=inStock.length; i+=1){

 var search = prompt("What item u want?");

  if(search === inStock[i]){
    print(search);

}else{

 alert("no item like"+search); 
}


function print(message) {
  document.write( '<p>' + message + 'is there in our shop'+'</p>');
}
script.js 
var temperatures = [100,90,99,80,70,65,30,10];
index.html 
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JavaScript Loops</title>
</head>
<body>
<script src="script.js"></script>
</body>
</html>

EDIT: Made code more viewable. - Dane E. Parchment Jr. (Moderator)

2 Answers

Dane Parchment
MOD
Dane Parchment
Treehouse Moderator 11,076 Points
Dane Parchment
Dane Parchment
Treehouse Moderator 11,076 Points

I believe that you need to subtract 1 from inStock.length.

When you call the length of a an array it will give you the actual number of elements, lets say 5.

However, based on array math, and computer science in general arrays start at the number 0, so here is a comparison of the ways that they would count if you start your count at 0:

  • Counting via inStock.length: 0, 1, 2, 3, 4, 5
  • How arrays count: 0, 1, 2, 3, 4

So as you can see in your loop you would be referencing a number 5, which does not exist in the array. So if you decrement your inStock.length by 1 you would get the desired results.

for(var i=0; i<=inStock.length-1; i+=1){
      //...do stuff here
}

Another way you can solve this without the extra math, is to change the less-than-or-equal-to operator to simply just less-than, this way it will only loop up to the value 1 less than the length of the array because the array length cannot be less than itself:

for(var i=0; i<inStock.length; i+=1){
      //...do stuff here
}
anuj maheshwari
anuj maheshwari
1,314 Points
anuj maheshwari
anuj maheshwari
1,314 Points

could you please write that piece of code

Dane Parchment
Dane Parchment
Treehouse Moderator 11,076 Points
Dane Parchment
Dane Parchment
Treehouse Moderator 11,076 Points

In the conditions for the for loop simply subtract 1 from inStock.length like so:

for(var i=0; i<=inStock.length-1; i+=1){
      //...do stuff here
}

Another way you can solve this without the extra math, is to change the less-than-or-equal-to operator to simply just less-than, this way it will only loop up to the value 1 less than the length of the array because the array length cannot be less than itself: 

for(var i=0; i<inStock.length; i+=1){
      //...do stuff here
}

I have added this code to my original answer.