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Strings

Here are a few examples of how you can declare a String in JavaScript, first using a string literal, followed by a call to the new operator and the String object's constructor function:

/*
 * JavaScript String Literals
 */
let s = 'some text'; // single-quotes
let s1 = 'some text'; // double-quotes
let s2 = `some text`; // template literal using back-ticks
let unicode =
  '中文 español Deutsch English देवनागरी العربية português বাংলা русский 日本語 ਪੰਜਾਬੀ 한국어 தமிழ் עברית'; // non-ASCII characters

/*
 * JavaScript String Constructor: `new String()` creates a new instance of a String
 */
let s3 = new String('Some Text');
let s4 = new String('Some Text');

If we want to convert other types to a String, we have a few options:

let x = 17;
let s = '' + x; // concatenate with a string (the empty string)
let s2 = String(x); // convert to String. Note: the `new` operator is not used here
let s3 = x.toString(); // use a type's .toString() method

Whether you use a literal or the constructor function, in all cases you will be able to use the various functionality of the String type.

String Properties and Methods​

  • s.length - will tell us the length of the string (UTF-16 code units)
  • s.charAt(1) - returns the character at the given position (UTF-16 code unit). We can also use s[1] and use an index notation to get a particular character from the string.
  • s.concat() - returns a new string created by concatenating the original with the given arguments.
  • s.padStart(2, '0) - returns a new string padded with the given substring until the length meets the minimum length given. See also s.padEnd().
  • s.includes("tex") - returns true if the search string is found within the string, otherwise false if not found.
  • s.startsWith("some") - returns true if the string starts with the given substring, otherwise false.
  • s.endsWith("text") - returns true if the string ends with the given substring, otherwise false.
  • s.indexOf("t") - returns the first index position of the given substring within s, or -1 if the substring is not found within s. See also s.lastIndexOf()
  • s.match(regex) - tries to match a regular expression against the string, returning the matches. See discussion of RegExp below.
  • s.replace(regex, "replacement") - returns a new string with the first occurrence of a matched RegExp replaced by the replacement text. See also s.replaceAll(), which replaces all occurrences.
  • s.slice(2, 3) - returns a new string extracted (sliced) from within the original string. A beginning index and (optional) end index mark the position of the slice.
  • s.split() - returns an Array (see discussion below) of substrings by splitting the original string based on the given separator (String or RegExp).
  • s.toLowerCase() - returns a new string with all characters converted to lower case.
  • s.toUpperCase() - returns a new string with all characters converted to upper case.
  • s.trim() - returns a new string with leading and trailing whitespace removed.

JavaScript Version Note: modern JavaScript also supports template literals, also sometimes called template strings. Template literals use back-ticks instead of single- or double-quotes, and allow you to interpolate JavaScript expressions. For example:

let a = 1;
let s = 'The value is ' + 1 * 6;
// Use ${...} to interpolate the value of an expression into a string
let templateVersion = `The value is ${1 * 6}`;