Document. getElementById

In js writing, you often need to obtain the id object. If you use getElementById directly to obtain the object, there are many codes and the old browser does not support this attribute. You can consider using the following code. For example, use _ $ (id) instead of document. getElementById (id ).
If it is a pure replacement, you can use the following code

The Code is as follows:

Function $ (id) {document. getElementById (id )}

For personal comparison, we recommend that you use prototype to define document. getElementById:

The Code is as follows:

Function $ ()
{
Var elements = new Array ();
For (var I = 0; I <arguments. length; I ++)
{
Var element = arguments [I];
If (typeof element = 'string ')
Element = document. getElementById (element );
If (arguments. length = 1)
Return element;
Elements. push (element );
}
Return elements;
}

You can also define it using the following code:

The Code is as follows:

Function $ (objectId ){
If (document. getElementById & document. getElementById (objectId )){
Return document. getElementById (objectId); // W3C DOM
} Else if (document. all & document. all (objectId )){
Return document. all (objectId); // MSIE 4 DOM
} Else if (document. layers & document. layers [objectId]) {
Return document. layers [objectId]; // NN 4 DOM .. note: this won't find nested layers
} Else {
Return false;
}
}

Writing in this way can save a lot of characters for the JS file and avoid input errors.
There is a small note that $ is a custom value. You can write any non-JavaScript reserved keywords, such as I _d and myid, according to your preferences. if the jQuery library file is called on your page, you can use $ instead of document. getElementById.