While loop incrementing array length

Question

Can someone please help me understand why the following array length increments without having a counter.

var inputName = "";
var namesArray = new Array();

while ( (inputName = prompt("Enter a name", "")) != "") {
    namesArray[namesArray.length] = inputName;
}

namesArray.sort();

var namesList = namesArray.join("\n");

console.log(namesList);

So from this I am assuming, a while loop increments any value you include inside the while loop. I had a look at MDN While Loop and I can see that both the x in this example is also incrementing.

I just want to be sure that I got this correct but mainly understand why it does this.

Thanks

the length is not a counter... once you put data in the array, the size increases — Kinnza
– Kinnza, Commented Dec 15, 2014 at 11:48
Doing assigment directly in the while loop, is generally not very good practice. — adeneo
– adeneo, Commented Dec 15, 2014 at 11:48

Icepickle · Accepted Answer · 2014-12-15 11:48:19Z

1

Adding an item into an array can be done in several ways in Javascript

your code essentially does a push, so you could replace

namesArray[namesArray.length] = inputName

with

namesArray.push(inputName)

answered Dec 15, 2014 at 11:48

Icepickle

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Comments

Amit Joki · Accepted Answer · 2014-12-15 11:47:47Z

0

For an empty array, length property will be 0. Let's put it like this

1st iteration

while ( (inputName = prompt("Enter a name", "")) != "") {
    namesArray[namesArray.length] = inputName;
    // namesArray[0] = inputName;
}

2nd iteration

while ( (inputName = prompt("Enter a name", "")) != "") {
    namesArray[namesArray.length] = inputName;
    // namesArray[1] = inputName; // since now length is 1
}

And so on.. So what you're doing is assigning in following fashion

names[0] = inputName
names[1] = inputName 
...

So, the length increases from 0 to n as you're adding elements to the Array.

answered Dec 15, 2014 at 11:47

Amit Joki

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2 Comments

Kam Miah Over a year ago

Thanks Amit. I like answers like this where examples are provided.

Amit Joki Over a year ago

@KamMiah ah! glad to have helped :)

Bob Brown · Accepted Answer · 2014-12-15 11:48:12Z

0

The length property of a Javascript array is the highest subscript plus one. So, if there are eight elements in an array, they have indices 0 - 7 and length is 8. The assignment statement, namesArray[namesArray.length] = inputName; adds an element to the array, and so increases the length.

answered Dec 15, 2014 at 11:48

Bob Brown

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Comments

Dhaval · Accepted Answer · 2014-12-15 11:48:46Z

0

   while (condition) {// Condition either return true or false so loop will execute untill condition return false
     namesArray[namesArray.length] = inputName //you just push data into array
    }

answered Dec 15, 2014 at 11:48

Dhaval

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1 Comment

A.L Over a year ago

Please edit your answer in order to add a context to the code (the comments are ok but it's not sufficient).

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