Is there a way to clone native functions in javascript like window.alert or document.write

What I want to do is change every alert in the code to a custom alert("you used alert");

var hardCodedAlert = alert; //I know this won't work.But what to do ?
 window.alert=function(){
 if(this.count == undefined)
 this.count=0;
 this.count=this.count+1;
 if(this.count == 1)
 hardCodedAlert("You used alert");
 };
 

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