如何在JavaScript中检查empty/undefined/null字符串？我在macOS v10.13.6(High Sierra) 上对 18 个选定的解决方案进行了测试。解决方案的工作方式略有不同（对于极端情况输入数据），如下面的代码片段所示。
In this tutorial, we are going to show you the ways of checking whether the JavaScript string is empty, undefined, or null. Just follow the guidelines.
Now go out there and check fornullwith confidence. Frequently Asked Questions What is a null check? In JavaScript, null represents an intentional absence of a value, indicating that a variable has been declared with a null value on purpose. On the other hand, undefined represents the absence ...
empty(),isset(), is_null()区别 empty 如果 变量 是非空或非零的值,则 empty() 返回 FALSE。...注意,isset对于NULL值变量,特殊处理。 is_null 检测传入值【值,变量,表达式】是否是null,只有一个变量定义了,且它的值是null,它才返回TRUE ...其它都返回 FALSE 代码片段: php $a; $b = false; $c...
Just as with keys - if an object has no values associated (not even an undefined/null) - it's empty: const isEmptyObject = (obj) => { return Object.values(obj).length === 0 && obj.constructor === Object; } console.log(isEmptyObject(emptyObject)); // true Using the Object.en...
undefinedandnullvalues sneak their way into code flow all the time. Whether we lose a reference through side-effects, forget to assign a reference variable to an object in memory, or we get an empty response from another resource, database or API - we have to deal withundefinedandnullvalues...
// 第一种方式let obj = {};// 第二种方式let obj2 =Object.create(null );// 第三种方式let obj3 =newObject(); 1.2设置对象的属性和方法 //1. “点号”法// 设置属性 obj.firstKey ="Hello World";// 获取属性 let key = obj.firstKey;//2. “方括号”法// 设置属性 ...
For example, isEmptyObject will return true for a Date or RegExp object. 1 console.log(isEmptyObject(Date.now())); //output: true 2 console.log(isEmptyObject(new RegExp())); //output: true Also, be careful because calling this method with a null or undefined value. They would ...
3.5.2 null null类型是只有一个值的数据类型,他表示此处的值现在为空,他表示一个空对象引用。 使用null类型值时注意以下几点: (1)使用typeof操作符测试null返回object字符串 var a = null; console.log(null); //null console.log(typeof null); //object 1. 2. 3. (2)undefined派生自null,所以等值比...
// Longhand if (test1 === true) or if (test1 !== "") or if (test1 !== null) // Shorthand //it will check empty string,null and undefined too if (test1) 注意:如果 test1 有任何值,它将在 if 循环后进入逻辑,该运算符主要用于 null 或undefined 的检查。 10.多个条件的 AND(&&)运...