JavaScript provides several ways to check if a variable is a string. One of the most common methods is to use thetypeofoperator, which returns the type of a variable. For example, the following code checks if a variable named “myVar” is a string: ...
To check if a variable is a string in JavaScript, use thetypeofoperator, e.g.typeof a === 'string'. If thetypeofoperator returns"string", then the variable is a string. For all other values, the variable is not a string. letname='Atta'if(typeofname==='string'){console.log(`V...
Javascript Boolean Type Introduction Using the typeof operator, we can check the datatype of a variable. If the variable is a Boolean value, typeof will return the string 'boolean'. Copy vara =Boolean(true);varb = false;//www.java2s.comvarc ="";vard = newDate();if(typeofa ==='...
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 ...
// 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。
We can use typeofoperatorto check the variable is defined or not. if (typeof variable !== 'undefined') { // the variable is defined } Solution 3: You can use this code: if (typeof variable === 'undefined') { // variable is undefined } ...
In JavaScript, users can use the equality operator (==) to check whether a variable is undefined or null. For example: leta;if(a ==null) {console.log('The variable is a null valued'); }else{console.log(a); } Output: Run Code ...
If you put a number in quotes, it will be treated as a text string. Example constpi =3.14; letperson ="John Doe"; letanswer ='Yes I am!'; Try it Yourself » Declaring a JavaScript Variable Creating a variable in JavaScript is called "declaring" a variable. ...
错误提示:开发工具(idea)提示:mutable variable is accessible from closure 浏览器报错提示: 可以正确执行的代码: var yy = document.getElementsByClassName("div_inTop_001"); for (var i = 0; i < yy.length; i++) { yy[i].addEventListener("mouseover", myfunction0000); yy[i].addEventListener("mo...
regexPattern.test(string); Here, “regexPattern” is a regular expression that will be checked in the given “string” using the test() method. Example In this example, first, we will create a regex pattern “/[a-zA-Z]/”, stored in a variable “pattern”: ...