In JavaScript, undefined is the default value for variables that have been declared but not initialized. On the other hand, null is an intentional assignment that explicitly indicates the absence of a value. Methods to Check if a Variable is Undefined Using typeof Operator Using Strict Equality...
If we dont assign the value to the variable while declaring, the JavaScript compiler assigns it to the undefined value. So, we can check that if the variable contains the null value or undefined value, it means we have a null variable....
Use the strict inequality (!==) operator to check if two strings are not equal, e.g. `a !== b`.
Now to check whether a given variable is a string or not, we'll use a JavaScript operator calledtypeof. Syntax: typeof variable; This operator returns the data type of the variable specified after it. If the variable is of string data type, it will return a string. Alternatively, it ca...
JavaScript recognizes false, 0, -0, 0n, "", null, undefined, and NaN as falsy.To verify that all values in an array are falsy, you can again use the every() method, but this time with a function that checks for falsy values:...
leta =null;console.log(_.isNull(a));// trueconsole.log(_.isUndefined(a));// falseconsole.log(_.isNil(a));// true Conclusion In this short guide, we've taken a look at how to check if a variable is null, undefined ornilin JavaScript, using the==,===andtypeofoperators, noting...
Whether you are a beginner or an experienced developer, this guide will help you navigate the nuances of variable checks in JavaScript. Method 1: Using the typeof Operator One of the simplest ways to check if a variable is undefined is by using the typeof operator. This operator returns a...
这部分表示执行名为 check_form 的 JavaScript 函数。通常在 HTML 元素的 href 属性或 onclick 事件中看到这种用法。void;：void 是一个 JavaScript 操作符，用于计算一个表达式但不返回值。在这里，0 被传递给 void 操作符，但实际上传递任何值都没有关系，因为 void 总是返回 undefined。使用 void ...
If it is, the paragraph will display the text "The property is undefined". The second paragraph uses the "v-else" directive to display the text "The property is defined" if the "email" property is not undefined.Vue Js Check object property Example 1 2 The property is undefined 3 The...
React Js Check String is Empty | null | undefined - Javascript Example 1 2 const App = () => { 3 const str = " "; 4 let message; 5 if (!str || str.trim() === "") { 6 message = "String is empty"; 7 } else { 8 message = "String has some Value "; 9 } 10 retu...