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;
            }
        }
    }
}