cheque de uso común js

Inspección digital

<input id="contractamount" name="projectList.contractamount" 
onblur="check(this)" onkeyup="value=value.replace(/[^\d\.]/g,'')" 
value="${projectList.contractamount}" type="text" maxlength="50">

    function check(e) {
        var re = /^\d+(?=\.{0,1}\d+$|$)/
        if (e.value != "") {
            if (!re.test(e.value)) {
                alert("请输入正确的数字");
                e.value = "";
                e.focus();
            }
        }
    }

Vacío o en blanco

var projectno = $("#projectno").val();

if(projectno === ""||projectno.split(" ").join("").length === 0){
			$.messager.alert('错误', '工程编号不能为空！');
		}