Javascript - Declare variables with a for loop

Question

I'm just wondering if it's possible to declare multiple variables using a for loop in Javascript.

Example: I have 4 <article> elements whose Ids are article1 article2 article3 and article4. Instead of declaring each variable independently, I'd like to do it in a loop (as they use essentially the same code and I don't want to repeat myself!).

Something like:

window.ready = function(){
    for (var i=1; i<=4; i++){

            var article[i] = document.getElementById("article" + i);

        }
}

The above returns an error with an unexpected [, so my syntax must be off (I'm very new to JS), but (a) is this on the right track and (b) will these be global variables if I run them in a window.ready function?

Felipe Oriani · Accepted Answer · 2016-09-08 13:07:39Z

6

You cannot set a variable name with [ char. Using it, you will get an exception of javascript. You can use a List/Array to do this, try with Array class, something like:

window.ready = function() {

   var articles = new Array();

   for (var i=1; i<=4; i++){

      articles[i] = document.getElementById("article" + i);

   }
}

With Array class, you are not required to specify the lenght, but if you want, you can set it on the constructor.

var articles = new Array(4);

Another approach is use the push method to add elements on the array, for sample:

window.ready = function() {

   var articles = []; // define an empty array

   for (var i=1; i<=4; i++){

      articles.push(document.getElementById("article" + i));

   }
}

edited Sep 8, 2016 at 13:07

answered Dec 13, 2012 at 10:47

Felipe Oriani

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2 Comments

JVG Over a year ago

Ah, cool. Just so I can get the syntax right in future, is it possible to call the variable i in the loop (like I've tried to do with var article[i])?

Felipe Oriani Over a year ago

@Jascination, using the keyword var you say to javascript that you want to declare, and as [ is a syntax error in the names of variables, you will have an exception. Because of this, I recommend you using an Array class, and with this, you can have as many as you want in the list. :)

isNaN1247 · Accepted Answer · 2012-12-13 10:48:52Z

4

Firstly its important to note that JavaScript functions have function scope rather than block scope meaning that 'article' is not unique to your for loop. Therefore declaring var article within your for block may be misleading as to what actually happens at runtime.

To achieve what you're after the following should work:

window.ready = function(){
    var article = [];
    for (var i=1; i<=4; i++){

            article.push(document.getElementById("article" + i));

        }
}

References

answered Dec 13, 2012 at 10:48

isNaN1247

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Comments

ddev · Accepted Answer · 2012-12-13 10:47:56Z

2

You are creating a new Article Array everytime you loop through..

Create an Article Array before entering your "for" loop.

article = new Array(4);
    for (var i=1; i<=article.length; i++){

            article[i] = document.getElementById("article" + i);

        }

answered Dec 13, 2012 at 10:47

ddev

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Comments

freakish · Accepted Answer · 2012-12-13 10:49:15Z

1

You can try using eval:

for (var i = 1; i <= 4; i++) {
    eval( 'var article'+i+' = document.getElementById("article' + i +'");' );
}

This will work like normal variables and they will be visible only in a local scope. This is probably a bad practice though, so just create an array or hash table to store dynamic variables.

answered Dec 13, 2012 at 10:49

freakish

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Comments

MrCode · Accepted Answer · 2012-12-13 10:52:07Z

1

Instead of that you could just grab all of the <article> elements:

var articles = document.getElementsByTagName("article");

// access them in a loop
for(var i=0; i<articles.length; i++)
{
    console.log("Hey I'm " + articles[i].id);
}

answered Dec 13, 2012 at 10:52

MrCode

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Comments

Sovan · Accepted Answer · 2012-12-13 10:49:23Z

0

Declare the array before using the array Ex : var article = []; // shorter version of new Array() then write your code as it is...

Hope this will help

answered Dec 13, 2012 at 10:49

Sovan

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