Number.isFinite 方法捕获所有有限数,是最适合我们的要求。 作者:Marcus Sanatan 译者:前端小智 来源:stackabuse 原文:https://stackabuse.com/java-check-if-variable-is-a-number/
How is it possible to determine if a variable value is a number?We have various ways to check if a value is a number.The first is isNaN(), a global variable, assigned to the window object in the browser:const value = 2 isNaN(value) //false isNaN('test') //true isNaN({}) /...
In JavaScript, a value can either be a primitive or an object. Therefore, you can check if a value is a JavaScript primitive (as opposed to being an object) using the following check: !(value instanceof Object) You may see value !== Object(value) as a means to check for prim...
How to Check if a Variable is an Array in JavaScript - To check if a variable is an array in Javascript is essential to handle data appropriately. We will discuss three different approaches to check if a variable is an array or not. We are having an arra
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 Value is a Negative Number Use the Math.sign() method to check if a value is a negative number. The Math.sign() method returns -1 if the provided argument is a negative number or can be converted to one. index.js function isNegative(num) { if (Math.sign(num) === -...
Method 1: Using the OR (||) operator to check undefined and null variable As discussed above, users can check if a variable is null or undefined using theOR (||)operator. It checks if the variable satisfies either of the two conditions. When users use it with two Boolean values, the ...
variable instanceof Array 1. This method runs about1/3 the speedas the first example. Still pretty solid, looks cleaner, if you're all about pretty code and not so much on performance. Note that checking for numbers does not work as variable instanceof Number always returns...
Variable Scope Solution 2: We can use typeofoperatorto check the variable is defined or not. if(typeofvariable !=='undefined') {// the variable is defined} Solution 3: You can use this code: if(typeofvariable ==='undefined') {// variable is undefined} ...
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...