①判断null: var exp = null; if (!exp && typeof exp != "undefined" && exp != 0) { alert("is null"); } //typeof exp != "undefined" 排除了 undefined; //exp != 0 排除了数字零和 false。 1. 2. 3. 4. 5. 6. 7. 更简单的正确的方法: var exp = null; if (exp === nul...
测试:https://www.runoob.com/try/try.php?filename=tryjs_undefined js判断字符串是否为""或null console.error(roomid);//roomid=null时console.error(roomid!='null'); roomid="";//roomid=""时console.error(roomid!=""); js中判断变量是否=“”和是否=null if(roomid !=""&& roomid !='nu...
let _isEmpty = (input) => {returninput+''==='null'||input+''==='undefined'||input.trim?input.trim()==='':input.replace(/^\s+|\s+$/gm,'')===''; };