08 - JavaScript - Strings

JavaScript strings are used to represent text data in a program. A string is a sequence of characters enclosed in quotes, either single quotes ('') or double quotes ("").

JavaScript String Concepts

Here are some concepts related to JavaScript strings -

1. Creating a string: To create a string, you can simply enclose a sequence of characters in quotes. For example:

    let str1 = 'Hello World';
    let str2 = "Welcome to JavaScript";
   

2. String length: The length property of a string returns the number of characters in the string. For example:

    let str = 'Hello World';
    console.log(str.length); // outputs 11
   

3. Accessing characters in a string: You can access individual characters in a string using the bracket notation. The index of the first character in a string is 0. For example:

    let str = 'Hello World';
    console.log(str[0]); // outputs 'H'
    console.log(str[6]); // outputs 'W'
   

4. Concatenating strings: You can concatenate (join) two or more strings together using the concatenation operator (+). For example:

    let str1 = 'Hello';
    let str2 = 'World';
    let result = str1 + ' ' + str2;
    console.log(result); // outputs 'Hello World'
   

5. Extracting substrings: You can extract a substring from a string using the substring() method. The method takes two arguments: the starting index and the ending index (optional). For example:

    let str = 'Hello World';
    let result = str.substring(0, 5); // extract the substring from index 0 to index 4
    console.log(result); // outputs 'Hello'
   

6. Converting to uppercase or lowercase: You can convert a string to uppercase or lowercase using the toUpperCase() and toLowerCase() methods, respectively. For example:

    let str = 'Hello World';
    console.log(str.toUpperCase()); // outputs 'HELLO WORLD'
    console.log(str.toLowerCase()); // outputs 'hello world'
   

7. Searching for a substring: You can search for a substring in a string using the indexOf() method. The method returns the index of the first occurrence of the substring, or -1 if the substring is not found. For example:

    let str = 'Hello World';
    console.log(str.indexOf('o')); // outputs 4
    console.log(str.indexOf('z')); // outputs -1
   

8. Replacing substrings: You can replace a substring with another string using the replace() method. The method takes two arguments: the substring to be replaced and the replacement string. For example:

    let str = 'Hello World';
    let result = str.replace('World', 'JavaScript');
    console.log(result); // outputs 'Hello JavaScript'
   

9. Splitting a string into an array: You can split a string into an array of substrings using the split() method. The method takes a delimiter as an argument, and the string is split at each occurrence of the delimiter. For example:

    let str = 'Hello,World';
    let arr = str.split(',');
    console.log(arr); // outputs ['Hello', 'World']
   

JavaScript String Methods

String Search Methods are used to search for a particular substring or pattern within a string in JavaScript.

Here are the details and examples for each of the following String Search Methods:

1. String indexOf(): The indexOf() method is used to search for the first occurrence of a substring within a string. If the substring is not found, the method returns -1. The method takes one required argument, which is the substring to search for. For example:

    let str = 'Hello World';
    console.log(str.indexOf('l')); // outputs 2
    console.log(str.indexOf('z')); // outputs -1
   

2. String lastIndexOf(): The lastIndexOf() method is similar to indexOf(), but searches for the last occurrence of a substring within a string. If the substring is not found, the method returns -1. The method takes one required argument, which is the substring to search for. For example:

    let str = 'Hello World';
    console.log(str.lastIndexOf('l')); // outputs 9
    console.log(str.lastIndexOf('z')); // outputs -1
   

3. String search(): The search() method is similar to indexOf(), but it takes a regular expression as its argument instead of a substring. The method searches for the first occurrence of the regular expression within the string, and returns the index of the first character of the match. If no match is found, the method returns -1. For example:

    let str = 'Hello World';
    console.log(str.search(/o/)); // outputs 4
    console.log(str.search(/z/)); // outputs -1
   

4. String match(): The match() method is used to search for a regular expression within a string. The method returns an array of all matches, or null if no matches are found. For example:

    let str = 'The quick brown fox jumps over the lazy dog';
    console.log(str.match(/o/g)); // outputs ['o', 'o', 'o']
    console.log(str.match(/z/g)); // outputs null
   

5. String matchAll(): The matchAll() method is similar to match(), but returns an iterator over all matches, including capture groups. The method returns a MatchAll iterator, which can be looped over using a for...of loop. For example:

    let str = 'The quick brown fox jumps over the lazy dog';
    let iterator = str.matchAll(/e/g);
    for (let match of iterator) {
      console.log(match);
    }
   

6. String includes(): The includes() method is used to check if a string contains a substring. The method returns true if the substring is found, and false otherwise. For example:

    let str = 'Hello World';
    console.log(str.includes('World')); // outputs true
    console.log(str.includes('JavaScript')); // outputs false
   

7. String startsWith(): The startsWith() method is used to check if a string starts with a particular substring. The method returns true if the string starts with the substring, and false otherwise. For example:

    let str = 'Hello World';
    console.log(str.startsWith('Hello')); // outputs true
    console.log(str.startsWith('World')); // outputs false
   

8. String endsWith(): The endsWith() method is used to check if a string ends with a particular substring. The method returns true if the string ends with the substring, and false otherwise. For example:

    let str = 'Hello World';
    console.log(str.endsWith('World')); // outputs true
    console.log(str.endsWith('Hello')); // outputs false
   

Summarizing Up

JavaScript strings are used to represent textual data in a program. A string is a sequence of characters enclosed in quotes, either single quotes ('') or double quotes (""). Strings are immutable, meaning that once a string is created, its contents cannot be changed.

Some of the key concepts related to JavaScript strings include creating strings, accessing characters in a string using bracket notation, concatenating strings using the + operator, extracting substrings using the substring() method, converting strings to uppercase or lowercase using the toUpperCase() and toLowerCase() methods, searching for substrings using the indexOf() method, replacing substrings using the replace() method, and splitting a string into an array using the split() method.

JavaScript strings can be used in a variety of applications, such as manipulating text input from users, formatting data for output, and generating dynamic HTML content. It's important to keep in mind that strings in JavaScript have a fixed length and are represented using Unicode characters, which can impact how they are displayed and processed in different contexts. Understanding these concepts can help you effectively work with strings in your JavaScript programs.