How can the current number of i be accessed in a for of loop?

Question

Given a for of loop the value of the assigned the variable(i for this example) is equal to what array[i] would equal if it was a normal for loop. H

Answer 1

Or

array = ["one", "two", "three"];

for (i = 0, item; item=array[i]; i++) {
  console.log(i); // Logs the current index number;
  console.log(item); // Logs the current item in the array;
}

Answer 2

You can use the entries function. It will return a index/value pair for each entry in the array like:

[0, "one"]
[1, "two"]
[2, "three"]

Use this in tandem with array destructuring to resolve each entry to the appropriate variable name:

const arr = ["one", "two", "three"]
for(const [index, value] of arr.entries()) {
  console.log(index, value);
}

Babel REPL Example

Answer 3

You can use the entries() function to get an iterator that includes the indices.

for (let [index, value] of [1, 2, 3].entries())
  console.log(index + ':' + value);

or, if you dont like the let [,] notation:

for (let entry of [1, 2, 3].entries())
  console.log(entry[0]+ ':' + entry[1]);

But what about other array-likes? Well, you could easily just take care of it yourself, really

let index = 0;
for (let ch of 'abcd') {
  ++index;
  //your code
}

Or, you can pretty easily patch in your own implementation

Object.defineProperty(String.prototype, 'indexerator', {get:function() {
    var elements = this[Symbol.iterator]();
    var index = 0;
    var output;

    return {
        [Symbol.iterator] : function() { return this; },
        next : function() {
            if (!(output = elements.next()).done)
                output.value = [index++, output.value];
            return output;
        }
    };
}});

/*other code*/

for (let [index, ch] of 'abcd'.indexerator)
  console.log(index + ':' + ch);

_{demonstrations}

Answer 4

nothing simple ... if you want "simple access" to both the item and the index in a loop over an array, use forEach e.g.

array.forEach(function(item, index) { 
... 
});

or as T.J. Crowder pointer out (and I missed the ES6 tag)

array.forEach((item, index) => { 
    ... 
});

like many programming languages, javascript has multiple ways to do similar things, the skill is in choosing the right tool for the job

Answer 5

use indexOf to get the index back

let array = ["one", "two", "three"];

for (let i of array) {
  console.log(i);
  console.log(array.indexOf(i));
}

NOTE: will only work for a array with no duplicates.

Answer 6

You mean this?

array = ["one", "two", "three"];

for (i = 0; i < array.length; i++) {
  console.log(i); // Logs the current index number;
  console.log(array[i]); // Logs the index matching in the array;
}

Also a good comment from Kaiido was that you can use this to get the value from the array directly as a variable.

for (var ind = 0, i=array[ind]; ind < array.length; i=array[++ind]) {
    console.log(i);
    console.log(ind);
}