GetElementByIdx_x js custom getElementById Function

Function Code:
Copy codeThe Code is as follows:
Document. getElementByIdx_x = function (id ){
If (typeof id = 'string ')
Return document. getElementById (id );
Else
Throw new error ('Please pass a string as a id! ')
}

Instance code:
Copy codeThe Code is as follows:
<Div id = 'box'> 9 </div>
<Script>
Document. getElementByIdx_x = function (id ){
If (typeof id = 'string ')
Return document. getElementById (id );
Else
Throw new error ('Please pass a string as a id! ')
}
Var timer = window. setInterval (function (){
Document. getElementByIdx_x ('box'). innerHTML = parseInt (document. getElementByIdx_x ('box'). innerHTML)-1;
If (parseInt (document. getElementByIdx_x ('box'). innerHTML) <0)
{
Window. clearInterval (timer );
Window. location = 'HTTP: // www.jb51.net ';
}
},1000 );
</Script>