TypeScript String

In TypeScript, the string is an object which represents the sequence of character values. It is a primitive data type which is used to store text data. The string values are surrounded by single quotation mark or double quotation mark. An array of characters works the same as a string.

Syntax

snippet
let var_name = new String(string);

Example

snippet
let uname = new String("Hello JavaTpoint");
console.log("Message: " +uname);
console.log("Length: "+uname.length);

Output:

Output
Message: Hello JavaTpoint Length: 16

There are three ways in which we can create a string.

1. Single quoted strings

It enclosed the string in a single quotation mark, which is given below.

Example

snippet
var studentName: String = 'Peter';

2. Double quoted strings

It enclosed the string in double quotation marks, which is given below.

Example

snippet
var studentName: String = "Peter";

3. Back-ticks strings

It is used to write an expression. We can use it to embed the expressions inside the string. It is also known as Template string. TypeScript supports Template string from ES6 version.

Example

snippet
let empName:string = "Rohit Sharma"; 
let compName:string = "JavaTpoint"; 
// Pre-ES6
let empDetail1: string = empName + " works in the " + compName + " company."; 
// Post-ES6
let empDetail2: string = `${empName} works in the ${compName} company.`; 
console.log("Before ES6: " +empDetail1);
console.log("After ES6: " +empDetail2);

Output:

Output
Before ES6: Rohit Sharma works in the JavaTpoint company. After ES6: Rohit Sharma works in the JavaTpoint company.

Multi-Line String

ES6 provides us to write the multi-line string. We can understand it from the below example.

Example

snippet
let multi = 'hello ' +
    'world ' +
    'my ' +
    'name ' +
    'is ' +
    'Rohit';

If we want that each line in the string contains "new line" characters, then we have to add "\n" at the end of each string.

Example

snippet
let multi = ' hello\n ' +
    'JavaTpoint\n ' +
    'my\n ' +
    'name\n ' +
    'is\n ' +
    'Rohit Sharma';
console.log(multi);

Output:

Output
hello JavaTpoint my name is Rohit Sharma

String Literal Type

A string literal is a sequence of characters enclosed in double quotation marks (" "). It is used to represent a sequence of character which forms a null-terminated string. It allows us to specify the exact string value specified in the "string literal type." It uses "pipe" or " | " symbol between different string value.

Syntax

snippet
Type variableName = "value1" | "value2" | "value3"; // upto N number of values

String literal can be used in two ways-

1. Variable Assignment

We can assign only allowed values to a literal type variable. Otherwise, it will give the compile-time error.

Example

snippet
type Pet = 'cat' | 'dog' | 'Rabbit';
let pet: Pet;
if(pet = 'cat'){
    console.log("Correct");
};
if(pet = 'Deer')
{
    console.log("compilation error");
};

Output:

Output
Correct compilation error

2. Function Parameter

We can pass only defined values to literal type argument. Otherwise, it will give the compile-time error.

Example

snippet
type FruitsName = "Apple" | "Mango" | "Orange";
function showFruitName(fruitsName: FruitsName): void {
    console.log(fruitsName);
}
showFruitName('Mango');   //OK - Print 'Mango'
//Compile Time Error
showFruitName('Banana');

Output:

Output
Mango Banana

String Methods

The list of string methods with their description is given below.

SN Method Description
1. charAt() It returns the character of the given index.
2. concat() It returns the combined result of two or more string.
3. endsWith() It is used to check whether a string ends with another string.
4. includes() It checks whether the string contains another string or not.
5. indexOf() It returns the index of the first occurrence of the specified substring from a string, otherwise returns -1.
6. lastIndexOf() It returns the index of the last occurrence of a value in the string.
7. match() It is used to match a regular expression against the given string.
8. replace() It replaces the matched substring with the new substring.
9. search() It searches for a match between a regular expression and string.
10. slice() It returns a section of a string.
11. split() It splits the string into substrings and returns an array.
12. substring() It returns a string between the two given indexes.
13. toLowerCase() It converts the all characters of a string into lower case.
14. toUpperCase() It converts the all characters of a string into upper case.
15. trim() It is used to trims the white space from the beginning and end of the string.
16. trimLeft() It is used to trims the white space from the left side of the string.
17. trimRight() It is used to trims the white space from the right side of the string.
18. valueOf() It returns a primitive value of the specified object.

Example

snippet
//String Initialization
let str1: string = 'Hello';
let str2: string = 'JavaTpoint';
//String Concatenation
console.log("Combined Result: " +str1.concat(str2));
//String charAt
console.log("Character At 4: " +str2.charAt(4));
//String indexOf
console.log("Index of T: " +str2.indexOf('T'));
//String replace
console.log("After Replacement: " +str1.replace('Hello', 'Welcome to'));
//String uppercase
console.log("UpperCase: " +str2.toUpperCase());

Output:

Output
Combined Result: HelloJavaTpoint Character At 4: T Index of T: 4 After Replacement: Welcome to UpperCase: JAVATPOINT
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