Methods to Check if a Variable is Undefined Using typeof Operator Using Strict Equality (===) Using Loose Equality (==) Using the void Operator Using a Custom Utility Function This article covers different ways to check if a variable is undefined, helping you write code that handles these ...
JavaScript Define a Function to Check If a Variable is a String 6 7 8 9 // Defining a function 10 function isString(myVar) { 11 return (typeof myVar === 'string'); 12 } 13 14 // Sample variables 15 var x = 10; 16 var y = true; 17 var z = "...
// Check if variable is equal to value if (username === "sammy_shark") { console.log(true); } 输出: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 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。 代码语言:javascr...
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...
let someVariable = 'Hello!' if (typeof somevariable === 'undefined') { console.log('Undefined variable'); } else if (typeof somevariable === 'null') { console.log('Null-value'); } else { console.log(somevariable); } Here, we're trying to check whether someVariable is null ...
Variable Scope Solution 2: 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 } ...
Since we want to check if a variable is a number, we will use the not operator, !, in our checks. Now let's check if the not operator and Number.isNaN() function can filter only numbers: > !Number.isNaN(intVar); true > !Number.isNaN(floatVar); true > !Number.isNaN(stringVar...
Checking if Boolean Is Primitive or ObjectA boolean literal (i.e. true or false) is a primitive. You can check this using the custom isPrimitive() function: console.log(isPrimitive(true)); // true console.log(isPrimitive(false)); // true ...
Function.prototype.partialApply=function() {varfunc =this; args =Array.prototype.slice.call(arguments);returnfunction() {returnfunc.apply(this, args.concat(Array.prototype.slice.call(arguments) )); }; }; 当我们希望引起您对代码块的特定部分的注意时,相关行或项目将以粗体显示: ...
varx;if(x===undefined){text='x is undefined';}else{text='x is defined';}console.log(text); Output: "x is undefined" Here we take an undefined variable name and compare it directly withundefinedwithout using any function or anything. But this method throws an error if we try to compa...