TypeScript - String
String is another primitive data type that is used to store text data. String values are surrounded by single quotation marks or double quotation marks.
let employeeName:string = 'John Smith';
//OR
let employeeName:string = "John Smith";
Template String
Since TypeScript version 1.4, TypeScript has included support for ES6 Template strings. Template strings are used to embed expressions into strings.
let employeeName:string = "John Smith";
let employeeDept:string = "Finance";
// Pre-ES6
let employeeDesc1: string = employeeName + " works in the " + employeeDept + " department.";
// Post-ES6
let employeeDesc2: string = `${employeeName} works in the ${employeeDept} department.`;
console.log(employeeDesc1);//John Smith works in the Finance department.
console.log(employeeDesc2);//John Smith works in the Finance department.
Here, instead of writing a string that is a combination of text and variables with concatenations, we can use a single statement with back-ticks `.
The variable values are written as ${. Using template strings, it is easier to embed expressions and also less tedious to write long text-based strings.
String methods
| Method | Description |
|---|---|
| charAt() | Returns the character at the given index |
| concat() | Returns a combination of the two or more specified strings |
| indexOf() | Returns an index of first occurrence of the specified substring from a string (-1 if not found) |
| replace() | Replaces the matched substring with a new substring |
| split() | Splits the string into substrings and returns an array |
| toUpperCase() | Converts all the characters of the string into upper case |
| toLowerCase() | Converts all the characters of the string into lower case |
| charCodeAt() | Returns a number that is the UTF-16 code unit value at the given index |
| codePointAt() | Returns a nonnegative integer Number that is the code point value of the UTF-16 encoded code point starting at the specified index |
| includes() | Checks whether a string includes another string |
| endsWith() | Checks whether a string ends with another string |
| LastIndexOf() | Returns the index of last occurrence of value in the string |
| localeCompare() | Checks whether a string comes before, after or is the same as the given string |
| match() | Matches a regular expression against the given string |
| normalize() | Returns the Unicode Normalization Form of the given string. |
| padEnd() | Pads the end of the current string with the given string |
| padStart() | Pads the beginning of the current string with given string |
| repeat() | Returns a string consisting of the elements of the object repeated in the given times. |
| search() | Searches for a match between a regular expression and a string |
| slice() | Returns a section of a string |
| startsWith() | Checks whether a string starts with another string |
| substr() | Returns a string beginning at the specified location and of the given characters |
| substring() | Returns a string between the two given indexes |
| toLocaleLowerCase() | Returns a lower case string while respecting current locale |
| toLocaleUpperCase() | Returns an upper case string while respecting current locale |
| trim() | Trims the white space from beginning and end of string |
| trimLeft() | Trims the white space from left side of the string |
| trimRight() | Trims the white space from right side of the string |
charAt()
The charAt() method returns a character at the specified index from a string.
character = str.charAt(index)
This method takes one number argument index and returns the character at the given index in the string.
let str: string = 'Hello TypeScript';
str.charAt(0); // returns 'H'
str.charAt(2); // returns 'l'
"Hello World".charAt(2); returns 'l'
concat()
The concat() method concatenates two or more specified strings.
str.concat(string2[, string3, ..., stringN])
This method takes two or more arguments of strings and returns a concatenation of the given strings.
let str1: string = 'Hello';
let str2: string = 'TypeScript';
str1.concat(str2); // returns 'HelloTypeScript'
str1.concat(' ', str2); // returns 'Hello TypeScript'
str1.concat(' Mr. ', 'Bond'); // returns 'Hello Mr. Bond'
indexOf()
The indexOf() method returns an index of first occurrence of the specified sub string from a string. The index starts from 0. It returns -1 if not found. the indexOf() method search is case-sensitive, so 't' and 'T' are different.
Optionally, you can specify an index as a second parameter to define where the searching should start from.
str.indexOf(searchValue[, fromIndex])
This method takes two arguments, the search string and an optional index number denoting the location the searching should start.
let str: string = 'TypeScript';
str.indexOf('T'); // returns 0
str.indexOf('p'); // returns 2
str.indexOf('e'); // returns 3
str.indexOf('T', 1); // returns -1
str.indexOf('t', 1); // returns 9
replace()
The replace() method replaces the matched substring with the specified string. The regular expression can also be used for searching.
str.replace(regexp|substr, newSubstr|function)
This method takes two arguments: a regex of string to be found, and the new string that will replace the existing substring.
let str1: string = 'Hello Javascript';
let str2: string = 'TypeScript';
str1.replace('Java', 'Type'); // returns 'Hello TypeScript'
str1.replace('JavaScript', str2); // returns 'Hello TypeScript'
str1.replace(/Hello/gi, 'Hi'); // returns 'Hi TypeScript'
split()
The split() method splits a string into substrings based on a specified separator character and returns an array of substrings.
str.split([separator[, limit]])
This method takes two arguments: a separator string and an optional limit specifying the number of entries to be found.
let str1: string = 'Apple, Banana, Orange';
let str2: string = ',';
str1.split(str2) // returns [ 'Apple', ' Banana', ' Orange' ]
str1.split(',') // returns [ 'Apple', ' Banana', ' Orange' ]
str1.split(',', 2) // returns [ 'Apple', ' Banana' ]
str1.split(',', 1) // returns [ 'Apple']
toUpperCase()
The toUpperCase() method returns an upper case representation of the string it is called on.
let str: string = 'Hello Typescript';
str.toUpperCase(); // returns 'HELLO TYPESCRIPT'
'hello typescript'.toUpperCase(); // returns 'HELLO TYPESCRIPT'
toLowerCase()
The toLowerCase() method returns a lower case representation of the string it is called on.
let str: string = 'Hello Typescript';
str.toLowerCase(); // returns hello typescript
'HELLO TYPESCRIPT'.toLowerCase(); // returns hello typescript