javascript - getting the size of a content box with javascriptHey -

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• why jquery or dom method such getelementbyid not find element? 6 answers

i trying width of content box following comand:

var box = document.getelementbyid('player'); var boxsize = box.clientwidth; 

it seems return something. when alert it gives out number. still throws error:

uncaught typeerror: cannot read property 'clientwidth' of null 

what happening here?

var box = document.getelementbyid('player'); if(box){   var boxsize = box.offsetwidth; }