javascript禁止输入数字

function onkeypressIsNumber(){
var mainForm = document.mainForm;//mainForm是form表单的ID
for(var i=0; i<mainForm.elements.length; i++){
if(mainForm.elements[i].type == "text"){
var element = mainForm.elements[i];
element.onkeypress = function(element){
var charCode = (element.which) ? element.which : event.keyCode;
if (charCode > 31 && (charCode < 48 || charCode > 57) && charCode != 46) {
return false;
}
return true;
}
}
}
}