TypeScript String
Strings are used to represent a sequence of Characters. Strings are immutable in TypeScript. When you perform operations on a String, TypeScript creates a new String. There are three ways in which you can create a String in TypeScript.
1. Double quoted strings: A String can be enclosed in double quotes as shown below.
let message: string = "Long long ago in a galaxy far far away"; console.log(message);Output:
Long long ago in a galaxy far far away
2. Single quoted strings: A String can also be enclosed in single quotes as shown below.
let message: string = 'Long long ago in a galaxy far far away'; console.log(message);Output:
Long long ago in a galaxy far far away
3. Back-ticks strings. We can write expressions using it: We can express a String inside backticks. This is useful when we have expressions inside our String. In the below example, we created an expression 2 raised to the power 3 inside backticks.
let message: string = `2 cube is $`; console.log(message);Appending strings: We can append strings using the + operator. In the below example, we appended three Strings using plus operator.
let str1: string = "Captain"; let str2: string = "Obvious"; let result: string = str1 + " " + str2; console.log(result);Output:
Captain Obvious
We can iterate over a TypeScript String using for..of loop. In the below example, we have a String representing vowels. We then iterated the String using for..of loop.
let vowels: string ="aeiou"; for(let vowel of vowels)
We can get the lower case by calling toLowerCase function. In the below example, we printed the String in lower case using toLowerCase function.
let letters: string = "Captain Skanda"; console.log(letters.toLowerCase());Output:
captain skanda
We can get the upper case by calling toUpperCase function. In the below example, we printed the String in upper case using toUpperCase function.
let letters: string = "Captain Skanda"; console.log(letters.toUpperCase());Output:
CAPTAIN SKANDA
We can find the length of string using length property. In the below example, we determined the length of the String using length property of the String.
let message: string = "TheQuickBrownForJumpedOverTheLazyDog"; console.log(message.length);Using trim function we can remove leading and trailing spaces. In the below example, we trimmed the leading and trailing spaces using trim function.
let letters: string = " Captain Cosmos "; console.log(letters.trim());Output:
Captain Cosmos
We can get character of a particular location either using index or using charAt function. In the below example, we are getting the character at position 3 using index operator as well as charAt function.
let message: string = "TheQuickBrownForJumpedOverTheLazyDog"; console.log(message[3]); console.log(message.charAt(3));startsWith function is used to check if a given string starts with given substring. In the below example, we used startsWith function to determine if a given String starts with «Captain».
let letters: string = "Captain Cosmos"; console.log(letters.startsWith("Captain"));endsWith function is used to check if a given string ends with given substring. In the below example, we used endsWith function to determine if a given String ends with «Cosmos».
let letters: string = "Captain Cosmos"; console.log(letters.endsWith("Cosmos"));We can use indexOf function to search for a substring within a string in TypeScript. In the below example, we are searching for a substring inside a given string and printing the result to the log.
let letters: string = "Captain Shyam"; console.log(letters.indexOf("Shy"));Please be informed that indexOf function returns -1 if the substring is not found as shown in the below example and output.
let letters: string = "Captain Shyam"; console.log(letters.indexOf("Shay"));includes method returns true or false depending on if the substring is found within the string. This is useful when we don’t really want a numeric output but just a boolean to indicate if the substring is found or not.
let letters: string = "Captain Shyam"; console.log(letters.includes("Shy")); console.log(letters.includes("Shay"));Substring — We can get substring of a given string using slice method. In the below example, we sliced a string to get a substring.
let letters: string = "Captain Cosmos"; console.log(letters.slice(0, 7)); console.log("");Using replace function we can replace instance of substring inside a string. In the below example, we replaced a substring with another string.
let letters: string = "Captain Cosmos"; letters = letters.replace("Cosmos", "Earth"); console.log(letters);Output:
Captain Earth
We can call split method on string to get array out of substrings. We need to specify to the split function the sequence which should be used to split the string. In the below example, we split the planet string on comma (,) to get the list of planets.
let planetStr: string = "Mercury,Venus,Earth,Mars,Jupiter"; let planets = planetStr.split(","); console.log(planets);Output:
Mercury,Venus,Earth,Mars,Jupiter
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TypeScript — Strings
The String object lets you work with a series of characters. It wraps the string primitive data type with a number of helper methods.
Syntax
var var_name = new String(string);
A list of the methods available in String object along with their description is given below −
Returns a reference to the String function that created the object.
Returns the length of the string.
The prototype property allows you to add properties and methods to an object.
String Methods
A list of the methods available in String object along with their description is given below −
Returns the character at the specified index.
Returns a number indicating the Unicode value of the character at the given index.
Combines the text of two strings and returns a new string.
Returns the index within the calling String object of the first occurrence of the specified value, or -1 if not found.
Returns the index within the calling String object of the last occurrence of the specified value, or -1 if not found.
Returns a number indicating whether a reference string comes before or after or is the same as the given string in sort order.
Used to match a regular expression against a string.
Used to find a match between a regular expression and a string, and to replace the matched substring with a new substring.
Executes the search for a match between a regular expression and a specified string.
Extracts a section of a string and returns a new string.
Splits a String object into an array of strings by separating the string into substrings.
Returns the characters in a string beginning at the specified location through the specified number of characters.
Returns the characters in a string between two indexes into the string.
The characters within a string are converted to lower case while respecting the current locale.
The characters within a string are converted to upper case while respecting the current locale.
Returns the calling string value converted to lower case.
Returns a string representing the specified object.
Returns the calling string value converted to uppercase.
Returns the primitive value of the specified object.