// 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
In JavaScript, a variable can be defined, but hold the valueundefined. if (typeof v === "undefined") { // no variable "v" is defined in the current scope // *or* some variable v exists and has been assigned the value undefined } else { // some variable (global or local) "v"...
letundefinedVar=undefined;if(undefinedVar===undefined){console.log("Variable has undefined value");} In the above example, theundefinedVarvariable will hit theifstatement because the value is equal toundefined. You don’t need thetypeofoperator when the variable is initialized. But if younever ...
Here's a Code Recipe to check whether a variable or value is either an array or not. You can use the Array.isArray() method. For older browser, you can use the polyfill 👍 constvariable=['🍝','🍜','🍲'];// ✅ NEWER BROWSERArray.isArray(variable);// 🕰 OLDER BROWSERObj...
leta;if(typeofa ==='undefined') {console.log('The variable is undefined '); }elseif(typeofa ==='null') {console.log('The variable is Null-value'); } Output: Run Code Explanation: The typeof operator specifies the type of the variable. However, users should note that if they chuc...
{value:"hello world",// 属性的值,默认为undefinedwritable:true,// 是否可修改,默认为falseenumerable:true,// 是否可枚举(遍历),默认为falseconfigurable:true// 表示对象的属性是否可以被删除,以及除 value 和 writable 特性外的其他特性是否可以被修改。});// 如果上面的方式你感到难以阅读,可以简短的写成...
[boolean] --check-leaks Check for global variable leaks [boolean] --delay Delay initial execution of root suite [boolean] --exit Force Mocha to quit after tests complete [boolean] --forbid-only Fail if exclusive test(s) encountered [boolean] --forbid-pending Fail if pending test(s) ...
In this example, we declare a variable myVar without assigning any value to it. When we check its type using typeof, we find that it is indeed “undefined”. This method is particularly useful because it won’t throw an error even if the variable hasn’t been declared at all. Instead,...
Like Python and JavaScript, RapydScript has exception handling logic. The following, for example, will warn the user if variable foo is not defined:try: print(foo) except: print("Foo wasn't declared yet") It's a good practice, however, to only catch exceptions we expect. Imagine, for ...
The second kind of undefined variable is one that has been declared but has never had a value assigned to it. If you read the value of one of these variables, you obtain its default value,undefined. This type of undefined variable might more usefully be calledunassigned, to distinguish it ...