input输入框只能输入正整数

<input type="text" value="1"  
    onkeyup="if(this.value.length==1){this.value=this.value.replace(/[^1-9]/g,'')}else{this.value=this.value.replace(/\D/g,'')}"  
    onafterpaste="if(this.value.length==1){this.value=this.value.replace(/[^1-9]/g,'0')}else{this.value=this.value.replace(/\D/g,'')}" />