log(isObjectEmpty(obj1)); // true const symbol = Symbol("key"); const obj2 = { [symbol]: "value" }; console.log(isObjectEmpty(obj2)); // false 在上面的示例中,isObjectEmpty()函数接受一个对象作为参数。函数内部使用Object.getOwnPropertySymbols(obj)获取对象的所有符号属性,并将它们存储...
// Undefined variableleta;if(a ==null) {console.log('Null or undefined value!'); }else{console.log(a); } This would check whetheraiseithernullorundefined. Sinceaisundefined, this results in: Null or undefined value! Though, we don't really know which one of these is it. If we were...
As discussed above, users can check if a variable is null or undefined using theOR (||)operator. It checks if the variable satisfies either of the two conditions. When users use it with two Boolean values, the OR operator will return a "true" value if it considers both conditions true. ...
javascriptCopyCodefunctionisObjectEmpty(obj) {for(letkeyinobj) {if(obj.hasOwnProperty(key)) {returnfalse;// 只要有一个属性存在,就返回false表示不为空} }returntrue;// 如果遍历完所有属性后仍然没有返回false,表示对象为空}// 测试对象是否为空constobj1 = {};console.log(isObjectEmpty(obj1));/...
letvalue;value// 👈 null and undefined check&&Object.keys(value).length===0&&value.constructor===Object;value=null;// nullvalue=undefined;// undefined B.低版本浏览器检查空对象 如果你需要兼容低版本浏览器。头疼,当我们在说低版本浏览器的时候,是指IE浏览器,好吧,我们还有两个选择可以解决这个问题...
// with jQueryvar isEmptyValue=function(value){var type;if(value==null){// 等同于 value === undefined || value === nullreturntrue;} type=Object.prototype.toString.call(value).slice(8,-1);switch(type){case'String':return!$.trim(value);case'Array':return!value.length;case'Object':re...
if(val===null||val==="") Example Here, we will create a variable “val” and assigned a “null” value to it: varval=null; Then, we will use the OR operator with strict equality operator in the “if” conditional statement to verify whether the variable is null or empty: ...
if(myVar){...} This way will evaluate totruewhenmyVarisnull, but it will also get executed whenmyVaris any of these: undefined null 0 ""(the empty string) false NaN if(myVar!==null){...} The above code is the right way to check if a variable isnullbecause it will be triggered ...
const obj = { import: "value" }; // 合法的,尽管 `import` 是保留字 class C { #import = "value"; } 关键字 关键字是JavaScript 中看起来像标识符但又具有特殊含义的标记。例如,在函数声明之前的 async 关键字表示该函数是异步的。 一些关键字是保留的,这意味着它们不能被用作变量声明、函数声明...
// Check if variable is equal to valueif(username==="sammy_shark"){console.log(true);} 输出: 代码语言:javascript 复制 true 如前所述,变量可以用来表示任何JavaScript数据类型。在本例中,我们将使用字符串、数字、对象、布尔值和null值声明变量。