Strings

The String Object

Javascript can convert strings into a String object, which includes:

• An array of each character in the string;
• An String.length property representing the number of characters in the string.
• A number of string methods that provide useful searching and manipulation functions. These methods will often accept or return the index of a character or substring.

Common string operations

• Find the 'length' of a string

  const browserType = 'mozilla';
  
  browserType.length; // 7
  

• Retrieving a specific string character

  const firstChar = browserType[0];
  
  console.log(firstChar); // 'm'
  

• Retrieving the last character

  const lastChar = browserType[browserType.length - 1];
  
  console.log(lastChar); // 'a'
  

Testing for a substring

The includes() method performs a case-sensitive search to determine whether one string may be found within another string, returning true or false as appropriate.

const browserType = 'mozilla';

if (browserType.includes('zilla')) {
  console.log('Found zilla!');
} else {
  console.log('No zilla here!');
}

Testing for a starting substring

The startsWith() method determines whether a string begins with the characters of a specified string, returning true or false as appropriate.

const browserType = 'mozilla';

if (browserType.startsWith('moz')) {
  console.log('Starts with moz!');
} else {
  console.log("Doesn't start with moz!");
}

Testing for an ending substring

The endsWith() method determines whether a string ends with the characters of a specified string, returning true or false as appropriate.

const browserType = 'mozilla';

if (browserType.endsWith('zilla')) {
  console.log('Ends with zilla!');
} else {
  console.log("Doesn't end with moz!");
}

Finding the location of a substring

The indexOf() method, given one argument: a substring to search for, searches the entire calling string, and returns the index of the first occurrence of the specified substring.

const paragraph = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

const searchTerm = 'dog';
const indexOfFirst = paragraph.indexOf(searchTerm);

console.log(`The index of the first "${searchTerm}" from the beginning is ${indexOfFirst}`);
// expected output: "The index of the first "dog" from the beginning is 40"

Updating parts of a string

The replace() method returns a new string with some or all matches of a pattern replaced by a replacement.

const browserType = 'mozilla';
const updated = browserType.replace('moz','van');

console.log(updated);      // "vanilla"
console.log(browserType);  // "mozilla"

Extracting a substring from a string

The slice() method extracts a section of a string and returns it as a new string, without modifying the original string.

const browserType = 'mozilla';
console.log(browserType.slice(1, 4)); // "ozi"

More String methods

See the complete list of Javascript string methods