How To Check If A String Is Empty/Undefined/Null in JavaScript

How To Check If A String Is Empty/Undefined/Null in JavaScript

If we want to check any string either it is filled or empty we can use Javascript for such purpose ... if (form.name.value == null ||. form.name.value == undefined ||.

To check if a string is empty or null or undefined in Javascript use the following js code snippet.

var emptyString;
if(!emptyString){
 // String is empty
}

In JavaScript, if the string is empty or null or undefined IF condition returns false.

var undefinedString;
if(!undefinedString){
 console.log("string is undefined");
}

var emptyString="";
if(!emptyString){
 console.log("string is empty");
}

var nullString=null;
if(!nullString){
 console.log("string is null");
}


check if a string is empty in JavaScript

If the string is not undefined or null and if you want to check for empty string in Javascript we can use the length property of the string prototype as shown below.

var emptyString="";
if(emptyString && emptyString.length==0){
  console.log("string is empty");
}


Or you can directly check for the empty string with javascript Comparison operator “===” as shown below.

if(emptyString===""){
 console.log("string is empty");
}

Thank you for reading !

JavaScript Strings | String concat() Method

JavaScript Strings | String concat() Method

JavaScript String concat() Method The concat() method is used to join two or more strings..we will explain the javascript string.concat() method with the definition of this method, syntax, parameters, and several examples.

In this tutorial, we will explain the javascript string.concat() method with the definition of this method, syntax, parameters, and several examples.

JavaScript String concat()

JavaScript concat() method, which is used to add or join or combine two or more strings together and it will return a new string.

Syntax

string.concat(string1, string2, string3, ...., stringX);

Parameters of string replace method

| Parameter | Description |
| string one, string two, string three, …, stringX | This is required. The strings to be combined or added |

Example:

Here we will take the first example of a javascript string concat() method. We have one string original string and we will add or join two more string in the original string using the concat() method.

var originalString = "JavaScript String, ";
var str1 = " Method The concat()";
var str2 = " Method is used to join two or more strings";
 
var res = originalString.concat(str1, str2);
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>JavaScript Strings | String concat() Method</title>
</head>
<body>
     
</body>
<script type = "text/javascript">
    var originalString = "JavaScript String, ";
    var str1 = " Method The concat()";
    var str2 = " Method is used to join two or more strings";

    var res = originalString.concat(str1, str2);

    document.write( "Output :- " + res ); 
</script>  

</html>

Result of the above code is:

Output :- JavaScript String, Method The concat() Method is used to join two or more strings

javaScript Replace() | javaScript String Replace All

javaScript Replace() | javaScript String Replace All

Javascript string replace() method. In this tutorial, we will explain the javascript string.replace() method with the definition of this method, syntax, parameters, and several examples.

Javascript string replace() method. In this tutorial, we will explain the javascript string.replace() method with the definition of this method, syntax, parameters, and several examples.

JavaScript String Replace()

Definition: – The JavaScript string replace() method searches a string for a specified value or a regular expression, or keyword, and replace match search string to given string, returns a new string

Syntax

string.replace(search_val, new_val);

Parameters of string replace method

| Parameter | Description |
| search_val | This is the first parameter and required. The value, or regular expression, that will be replaced by the given value |
| new_val | This is the second parameter and required. The given value to replace the search value. |

Ex:

   var str = "My fav bike color is white";
   var res = str.replace(/white/g, "black");
   document.write( "Output :- " + res ); 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>javaScript Replace() |javaScript String Replace All</title>
</head>
<body>
     
</body>
<script type = "text/javascript">
   var str = "My fav bike color is white";
   var res = str.replace(/white/g, "black");
   document.write( "Output :- " + res ); 
</script>  

</html>

Result of the above code is:

Output :- My fav bike color is black

Ex

Here we will take the second example of string replace() method with case-insensitive string:

   var str = "My fav bike color is White";
   var res = str.replace(/white/gi, "black");
   document.write( "Output :- " + res ); 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>javaScript Replace() |javaScript String Replace All</title>
</head>
<body>
     
</body>
<script type = "text/javascript">
   var str = "My fav bike color is White";
   var res = str.replace(/white/gi, "black");
   document.write( "Output :- " + res ); 
</script>  

</html>

Result of the above code is:

Output :- My fav bike color is black

Ex3

Here we will take a new example of javascript string replace all with regexp.

var str = 'this is the sentence to end all sentences';
 
var res = str.replace(new RegExp('sentence', 'g'), 'message');
 
document.write( "Output :- " + res ); 
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>javaScript Replace() |javaScript String Replace All</title>
</head>
<body>
  <script type = "text/javascript">
     
   var str = 'this is the sentence to end all sentences';
 
   var res = str.replace(new RegExp('sentence', 'g'), 'message');
 
   document.write( "Output :- " + res ); 
 
  </script>  
</body>
</html>

Result of the above code is:

Output :- this is the message to end all messages

JavaScript String Methods You should know | JavaScript Tutorial

JavaScript String Methods You should know  | JavaScript Tutorial

In this javascript string methods tutorial. We will explain the most useful and important javascript string methods. Javascript string methods help to work with strings in javascript.

In this javascript string methods tutorial. We will explain the most useful and important javascript string methods. Javascript string methods help to work with strings in javascript.

We will demonstrate javascript string methods like javascript string replace, javascript string contains, javascript string length, javascript string concatenation, javascript string substring, remove the character from string javascript, javascript string uppercase, javascript string lowercase, string trim, tostring method, a match in the string, split string in javascript,
javascript string substr, trim string, array to comma-separated string, etc

We need to know some of the most important and useful javascript string methods.

Let’s see JavaScript String Methods

Important String Methods in javaScript

  • Length Method
  • toLocaleLowerCase() Method
  • toLocaleLowerCase() Method
  • indexOf() Method
  • search() Method
  • slice() Method
  • substring() Method
  • substr() Method
  • replace() Method
  • includes() Method
  • concat() Method
  • charAt() Method
  • charCodeAt() Method
  • lastIndexOf() Method
  • trim() Method
  • match() Method
  • split() Method
  • toString() Method
  • valueOf() Method

1. length() Method

It is used to count the number of characters in a string javascript.

Example

var str = "Hello Morioh";
var x = str.length;

Output

// return 
12

2. toLocaleLowerCase() Method

The javascript toLocaleLowerCase() is used to changed string into lower case.

Example

var str = "Hello Morioh";
var res = str.toLocaleLowerCase();

Output

// return
hello morioh

3. toLocaleUpperCase() Method

The javascript toLocaleUpperCase () is used to changed string into upper case.

Example

var str = "Hello Morioh";
var res = str.toLocaleUpperCase();

Output

// return
HELLO MORIOH

4. indexof() Method

The indexof () method returns the first position of a specified value in a string.

Example

var txt = "Connecting with Programmers and Developers all over the World";
 var test = txt.indexOf("over");

Output

// return 
47

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5. search() Method

The javascript search () method searches a string for the specified value, and returns the status of the match.

Example

var str = "Hello Morioh";
var res = str.search("Morioh");

Output

//Return
6

6. slice() Method

The slice () method removes the parts of a string and returns the extracted parts to a new string.

Use the Start and End Ultimate to specify the part of the string that you want to remove.

Example

var str = "JavaScript String Methods"; 
var res = str.slice(0, 10);

Output

// return
JavaScript

7. substring() Method

The Javascript substring() method is used to removes the characters from one string, between two specified indices, and returns the new substring.

Example

var str = "JavaScript String Methods"; 
var res =  str.substring(1, 4);

Output

//return
ava

8. substr() Method

A string substr() method begins on the character in the specified position, and returns the specified number of characters.

Example

var str = "JavaScript String Methods"; 
var res =  str.substr(1, 4);

Output

//return
avaS

9. replace() Method

The Javascript replace() changes the defined value to an another value:

Example

var str = "JavaScript String Methods"; 
var res = str.replace("Methods", "Tutorial");

Output

// return
JavaScript String Tutorial

10. includes() Method

The includes() method is used to determine whether a string contains the characters of a specified string or not. If is exist return true or not return false.

Example

var str = "Hello world, my name is morioh.";
var res = str.includes("name");

Output

// return 
True

11. concat() Method

The concat() method is used for join two or more strings.

Example

var str1 = "Hello ";
var str2 = "morioh!";
var res = str1.concat(str2);

Output

// return
Hello morioh!

12. charAt() Method

The Javascript charAt() is used to take a character to a described index location:

Example

var txt = "Hello Dev";
var res = txt.charAt(0);

Output

// return
H

13. charCodeAt() Method

The charCodeAt() method returns the Unicode of the character at a specified index in a string:

Example

var str = "TEST";
str.charCodeAt(0); 

Output

// return
84

14. lastIndexOf () Method

The lastIndexOf() the method returns the index of the last occurrence of a specified text in a string:

Example

var str = "Your are talented dev";
var pos = str.lastIndexOf("dev");

Output

// return
18

16. trim() Method

The javascript trim() method removes whitespace from both sides of a given string:

Example

var str = "        javascript trim() method removes whitespace        ";
alert(str.trim());

Output

// return
javascript trim() method removes whitespace

match() Method

The match() method searches a string for a match against a regular expression, and returns the matches, as an Array object.

Example

 var str = "lopersum lopersum lopersum lopersum."; 
 var res = str.match(/sum/g);

Output

// return
 sum,sum,sum,sum

17. split Method

The javascript split method, which is used to convert string to an array:

Example

var str = "1,2,3,4,5";
var arr = str.split(",");
document.write(arr[0]);
document.write("<br>");
document.write(arr[1]);
Output
// return
1
2

toString() Method

The javascript toString() method returns the value of a String object.

Example

var str = "javaScript World!";
var res = str.toString();

Output

// return
javaScript World!

18. valueOf() Method

The javascript valueOf() method, which is used to gets the primitive value of a String object.

Example

var str = "javaScript World!";
 var res = str.valueOf();

Output
// return
javaScript World!

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JavaScript | String indexOf() Method