dom - JavaScript document.getElementById(“id”) and element id attribute - Stack Overflow

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I have:

<div id="myDiv1"></div>
<div id="myDiv2"></div>

In JavaScript, I can set div innerHTML by writing:

myDiv1.innerHTML = "myDiv1, Hi!"

or

document.getElementById("myDiv2").innerHTML = "myDiv2, Hi!"

Why should I use document.getElementById when I can simply use element Id ? Is this working every time or only in some special scenarios (like simple sample)?

thanks,

Mike

I have:

<div id="myDiv1"></div>
<div id="myDiv2"></div>

In JavaScript, I can set div innerHTML by writing:

myDiv1.innerHTML = "myDiv1, Hi!"

or

document.getElementById("myDiv2").innerHTML = "myDiv2, Hi!"

Why should I use document.getElementById when I can simply use element Id ? Is this working every time or only in some special scenarios (like simple sample)?

thanks,

Mike

• javascript
• dom

Share Improve this question Follow edited Feb 5, 2015 at 10:06 T.J. Crowder 1.1m200200 gold badges2k2k silver badges1.9k1.9k bronze badges asked Feb 5, 2015 at 10:00 mike mmike m 13511 silver badge99 bronze badges 5

• In your first snippet, you are using myDiv1. How have you retrieved it? – Giorgio Commented Feb 5, 2015 at 10:03
• 1 No, you can't. Just you can assign to var every one div by ID, but nothing without this assignment. – pavel Commented Feb 5, 2015 at 10:03
• 1 This does work, but it's a bad idea. – lonesomeday Commented Feb 5, 2015 at 10:04
• It is true that browsers expose elements with ids as global variables. But this is not reliable and error prone, as any globals in general. Plus there is no guarantee that older browsers will do the same. – dfsq Commented Feb 5, 2015 at 10:04
• @Giorgio: It's an automatic global, because the element has an id. – T.J. Crowder Commented Feb 5, 2015 at 10:04

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2 Answers 2

Sorted by: Reset to default 8

Why should I use document.getElementById when I can simply use element Id ?

To avoid conflicts. The global namespace on browsers is incredibly crowded, all sorts of things are dumped in there, including (as you've found) globals referring to any element with an id (so-called "automatic globals").

In contrast, getElementById only does what it says, finds an element by its id; it's more constrained. (Other than bugs in old versions of IE, which also looked at elements with name attributes.)

when you write

myDiv1.innerHTML = "myDiv1, Hi!"

you are calling window object, so actual call is like this

window.myDiv1.innerHTML = "myDiv1, Hi!"

This behavior is deprecated now and to be avoided. Instead we should use

document.getElementById` 

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