A detailed explanation of document.all usage

All[] has been superseded by the standard getElementById () method and the getElementsByTagName () method of the document interface and the Getelementsbyname () method of the Document object.
However, this all[] array is still used in existing code.

One.
Document.all is a collection of all elements within a page. For example:
document.all (0) represents the first element within a page
Two.
Document.all can tell if the browser is IE
if (document.all) {
Alert ("is ie!");
}
Three.
You can also set the ID property (ID=AAAA) for an element and then call the element with DOCUMENT.ALL.AAAA
Four.
Case:

Code Listing 1:
<input name=aaa value=aaa>
<input id=bbb value=bbb>
<script language=jscript>
Alert (Document.all.aaa.value)//Take value by name
Alert (Document.all.bbb.value)//Based on ID take value
</script>
Code Listing 2:
But often the name can be the same (for example, using a checkbox to take a user's many hobbies)
<input name=aaa value=a1>
<input name=aaa value=a2>
<input id=bbb value=bbb>
<script language=jscript>
Alert (DOCUMENT.ALL.AAA (0). Value)//display A1
Alert (DOCUMENT.ALL.AAA (1). Value)//Display A2
Alert (DOCUMENT.ALL.BBB (0). Value)//This line of code will fail
</script>
Code Listing 3:
In theory, the IDs in a page are not the same, if there are different tags have the same id
Document.all.id will fail, just like this:
<input id=aaa value=a1>
<input id=aaa value=a2>
<script language=jscript>
Alert (Document.all.aaa.value)//show undefined instead of A1 or A2
</script>
Code Listing 4:
For a complex page (the code is very long, or the ID is generated automatically by the program), or a
JavaScript Beginners Write the program, it is likely to appear two tags have the same ID case.
In order to do the programming without error, I recommend this way:

<input id=aaa value=aaa1>
<input id=aaa value=aaa2>
<input name=bbb value=bbb>
<input name=bbb value=bbb2>
<input ID=CCC value=ccc>
<input name=ddd value=ddd>

<script language=jscript>
Alert (document.all ("AAA", 0). Value)
Alert (document.all ("AAA", 1). Value)
Alert (document.all ("BBB", 0). Value)
Alert (document.all ("BBB", 1). Value)
Alert (document.all ("CCC", 0). Value)
Alert (document.all ("ddd", 0). Value)
</script>

A detailed explanation of document.all usage