Excuse me, why doesn't setTimeout () work?

<div class="panel" @mousemove="mv1">debounce=========={{msg1}}</div>

is a piece of code written in the vue component

    mv1:function(e){
    var timer ;
    clearTimeout(timer);
    timer = setTimeout(this.msg1PP,5000);

    }

Why doesn"t this code have the effect of debounce? Is the number of
increasing?

Mar.31,2021

  mv1:function(e){
    var timer ;
    clearTimeout(timer);
    timer = setTimeout(() => this.msg1PP,5000); // 

    }
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