Example 2 : React check if string is null or empty In this second example of this tutorial, we use React JS to check if a string is empty or null using a simple condition. The condition is !str || str.trim() === "", which means that the string is either falsy (such as null,...
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。
After moving the space, we can check that if the strings length is zero, the string can be either empty, null, or undefined.SyntaxBelow is the syntax given to check the empty string using the trim() method.if(string_name.trim() === ''){ // string is empty } ...
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.
function isEmpty(obj){ if(typeof obj == "undefined" || obj == null || obj == ""){ return true; }else{ return false; } } 1. 2. 3. 4. 5. 6. 7. 参考二: if (variable1 !== null || variable1 !== undefined || variable1 !== '') { ...
而null是代表了缺失对象引用。js是不能给null设置变量或者对象属性的。一些原生方法像String.prototype.match()会返回null来表示缺失对象,看一下下面这个例子: letarray =null; array;// => nullletmovie = {name:'Starship Troopers',musicBy:null};
With the constructor, you can check if an object is aDate: Example (myDate.constructor=== Date); Try it Yourself » All Together typeof"John"// Returns "string" typeof("John"+"Doe")// Returns "string" typeof3.14// Returns "number" ...
// TypeError: Cannot covert undefined or null ot objectgoodEmptyCheck(undefined);goodEmptyCheck(null); #Improve empty check fornullandundefined If you don't want it to throw aTypeError, you can add an extra check: letvalue;value// 👈 null and undefined check&&Object.keys(value).length==...
Once again, this method will fail on a null or undefined input. 3. JSON.stringify The JSON.stringify method is used to convert a JavaScript object to a JSON string. So we can use it to convert an object to a string, and we can compare the result with {} to check if the given ...
对于不包含大逻辑的 if-else 条件,可以使用下面的快捷写法。我们可以简单地使用三元运算符来实现这种简化。 如果有嵌套的条件,可以这么做。 3. if 判断值是否存在 这是我们都在使用的一种常用的简便技巧,在这里仍然值得再提一下。 注意:如果 test1 有值,将执行 if 之后的逻辑,这个操作符主要用于 null 或 unde...