The typeof operator can be used to check if a variable is undefined by comparing its type with the string ‘undefined’. Here is an example of the code. let a; console.log(typeof a === 'undefined'); // true This method is safe because it won’t throw an error if the variable ...
Example 3 : vue js check if string is empty In this third example of this tutorial, we use Vue.js programming language to check if a string is empty or null, undefined using `str && str.trim() !== ""`. This is a common task when we want to validate user input or filter out ...
console.log("空string值是null值吗?用===判断,答案为:" + ("" ===null)); console.log("空string值是undefined值吗?用==判断,答案为:" + ("" ==undefined)); console.log("空string值是undefined值吗?用===判断,答案为:" + ("" ===undefined));console.log("空string值是0值吗?用==判断,...
问Javascript - if (变量)检查'undefined‘失败ENundefined 是 Undefined 类型的唯一值，它表示未定义的...
if(str.match(reg)){ //包含; } 方法三: search()方法可在字符串内检索指定的值,或找到一个或多个正则表达式的匹配。 var str = "123" console.log(str.search("2") != -1); // true RegExp对象的方法search() 方法用于检索字符串中指定的子字符串,或检索与正则表达式相匹配的子字符串。如果没有...
One of the simplest ways to check if a variable is undefined is by using the typeof operator. This operator returns a string that indicates the type of the unevaluated operand. If the variable is not defined, typeof will return the string “undefined”. Here’s how you can use it: let...
When the value is absolutely not present in the variable or string or anything else, we call it as Undefined. In JavaScript, undefined is a one of the primitive data type. It is used to represent the absence of a value. It get assigned to a variable when it is declared but not ...
The variable is not a String. Example 2:str = "That is your place."; if (typeof(str) === 'string') { console.log('The variable is a String.'); } else { console.log('The variable is not a String.'); } Output:The variable is a String. ...
We can use search method to check if a string contains a substring or not as shown below. var actualstring = "Javascript search method", var substringToCheck = "search"; var isContains=actualstring.search("search") !== -1; //isContains true ...
If you want to check whether the string is empty/null/undefined, use the following code:let emptyStr; if (!emptyStr) { // String is empty }If the string is empty/null/undefined if condition can return false: Javascript empty string...