Published on 2021-08-10, by Javed Shaikh
In this post I am going to show how I normally do validation for empty string. We are going to check string with different values such as blank, undefined, null and white spaces. We will go one by one with examples.
To see if a string is null or undefined, we can simply use below snippet to check. Here we are using logical NOT operator to identify is a const variable str holds a string.
1const str1 = null
2const str2 = undefined
3
4if (!str1 || !str2){
5 console.log("This is empty!, i.e. either null or undefined")
6}The above snippet will print "This is empty, i.e. either null or undefined". The above code works for both null,undefined and empty string like "".
Next, we are going to check if string is blank or having some white spaces.
1const str3 =" "
2if (!str3.trim()){
3 console.log("Its not an empty string")
4}Here we are using JavaScript's trim() function to remove all the white spaces from both ends of the string and then check if its empty.
Lets combine both checks and include these in our own utility function so that we can use it repeatedly anywhere we need.
1const isEmpty = (str) => !str || !str.trim();In above snippet, we are using JavaScript's arrow function to minimize lines of code. Here we have two checks, the first one will check for all null, empty and undefined strings and the second check is for white space characters. The above function will return true if a string is empty or false if not.
Lets use some demo to check how this function works.
1 //function to check if a string is empty
2 const isEmpty = (str) => !str || !str.trim();
3
4 const str1 = null; //null
5 const str2 = ""; //empty
6 const str3 = undefined; //undefined
7 const str4 = " "; //white space
8 const str5 = 0; //0
9 const str6 = "shaikhu"; //shaikhu
10
11 console.log(isEmpty(str1)); // true
12 console.log(isEmpty(str2)); // true
13 console.log(isEmpty(str3)); // true
14 console.log(isEmpty(str4)); // true
15 console.log(isEmpty(str5)); // true
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