Javascript forEach() through an array: how to get the previous and next item?

Question

Let's say we have an array of objects like:

var fruits = [ {name:"banana", weight:150},{name:"apple", weight:130},{name:"orange", weight:160},{name:"kiwi", weight:80} ]

I want to iterate through fruits and tell each time the name of the current, the previous and the next fruit. I would do something like:

fruits.forEach(function(item,index) {
console.log("Current: " + item.name);
console.log("Previous: " + item[index-1].name);  
console.log("Next: " + item[index-1].name);
});

But obviously it doesn't work for next and previous items... Any idea?

Please note that I do not want to use the classic for loop

(for i=0; i

Thanks a lot!

'item' holds only current object in forEach method. If you know any index, then use array[index] to get the value. — Ganesh Babu
– Ganesh Babu, Commented Aug 1, 2016 at 10:51

Nehal Gala · Accepted Answer · 2016-08-03 09:55:32Z

51

Its not working because item is not an array so we cannot write item[index-1].name. Instead, we need to use fruits[index-1] .Also, the first element of the array will not have the previous item and the last element will not have next item. Code snippet below should work for you.

var fruits = [{
    name: "banana",
    weight: 150
}, {
    name: "apple",
    weight: 130
}, {
    name: "orange",
    weight: 160
}, {
    name: "kiwi",
    weight: 80
}]

fruits.forEach(function(item, index) {
    console.log("Current: " + item.name);
    if (index > 0) {
        console.log("Previous: " + fruits[index - 1].name);
    }
    if (index < fruits.length - 1) {
        console.log("Next: " + fruits[index + 1].name);
    }
});

edited Aug 3, 2016 at 9:55

answered Aug 1, 2016 at 10:58

Nehal Gala

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Comments

kevin ternet · Accepted Answer · 2016-08-01 16:50:35Z

14

Callback function in ForEach loop accepts the array as third parameter :

fruits.forEach((item, index, arr) => {
    console.log("Current: " + item.name);
    console.log("Previous: " + ((0 === index)? "START" : arr[index-1].name));
    console.log("Next: " + ((arr.length - 1 === index)? "END" : arr[index+1].name));
});

answered Aug 1, 2016 at 16:50

kevin ternet

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Comments

guysigner · Accepted Answer · 2016-08-01 10:57:51Z

6

For the first and last item, you can log END, or you can make it a carousel.

option 1: mark the start and the end:

fruits.forEach(function(item,index) {
  console.log("Current: " + item.name);
  console.log("Previous: " + (0 == index)? "START" : fruits[index-1].name);  
  console.log("Next: " + (fruits.length - 1 == index)? "END" : fruits[index+1].name);
});

option 2: carousel

fruits.forEach(function(item,index) {
      console.log("Current: " + item.name);
      console.log("Previous: " + (0 == index)? fruits[fruits.length - 1].name : fruits[index-1].name);  
      console.log("Next: " + (fruits.length - 1 == index)? fruits[0].name : fruits[index+1].name);
    });

answered Aug 1, 2016 at 10:57

guysigner

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Comments

James · Accepted Answer · 2016-08-01 11:00:49Z

6

fruits.forEach(function(item,index) {
  console.log("Current: " + item.name);
  if (index > 0) {
    console.log("Previous: " + fruits[index-1].name);  
  }
  if (index < (fruits.length - 1)) {
    console.log("Next: " + fruits[index+1].name);
  }
});

edited Aug 1, 2016 at 11:00

answered Aug 1, 2016 at 10:48

James

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2 Comments

a_nain Over a year ago

would fail for 0th index and sparse array values :)

James Over a year ago

@you.know.nothing Thanks for pointing it out. Didn't think of it.

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