We can create strings in different ways:
//directly assign to a variable or string constant
const name = "Alexander";
//create a string using the constructor String
const name = new String("Alexander");
The String object has a large set of properties and methods with which we can manipulate strings.
lenght – specifies the length of the string
const name = "Alexander";
console.log(hello.length);//8
repeat – repeats a string
The repeat() method allows you to create a string by repeating another string multiple times. The number of repetitions is passed to as an argument.
const name = "Alexander";
console.log(name.repeat(2)); //AlexanderAlexander
Methods for searching in a string
indexOf() – search for the first substring
To search for some substring in a string, use the indexOf() methods (index of the first occurrence of the substring)
const hello = "Hello, my name Alexander";
const firststring = hello.indexOf("name");
console.log(firststring)//12
lastIndexOf() – looking for the last substring
Similar to the indexOf() method, but with the difference that this method looks for the index of the last occurrence of a substring.
const hello = "Hello, my name Alexander. Second name - Arthur";
const lastststring = hello.lastIndexOf("name");
console.log(firststring)//34
includes – returns true if the string contains a specific substring
const hello = "Hello, my name Alexander";
console.log(hello.includes("name")); // true
console.log(hello.includes("Second")); // false
Cut substring from string
substring – cut the string by index
The substring() method takes two parameters:
- The index of the character in the string, starting from which the string should be trimmed.
- The index to which the string should be cut. Optional parameter – if it is not specified, then the rest of the string is truncated.
const hello = "Hello, my name Alexander";
const world = hello.substring(9, 10);
console.log(world); //my
slice – cuts out part of a substring
The slice method also allows you to get some part of a string from it. It takes two parameters:
- Сharacter index in the string, starting from which the string should be trimmed.
- The index to which the string should be trimmed. If it is not specified, then the rest of the string is truncated.
const hello = "Hello, my name Alexander";
const world = hello.slice(9, 10);
const world2 = hello.slice(9,);
console.log(world); //my
console.log(world2); //my name Alexander
Substring() and slice() are very similar methods, but there are some differences between them:
- In slice(), the start index must be less than the end index;
- In substring(), if the start index is greater than the end index, then they are swapped.
- slice() allows negative indexes. A negative index indicates the character index relative to the end of the string.
- substring() doesn’t support negative indexes
Changing the case of a string
toLowerCase – converts a string to lower case
const hello = "Hello, my name Alexander";
console.log(hello.toLowerCase()); //hello, my name alexander
toUpperCase – converts string to uppercase
const hello = "Hello, my name Alexander";
console.log(hello.toUpperCase()); //HELLO MY NAME ALEXANDER
Getting a character by index
charAt – returns character by index
const hello = "Hello, my name Alexander";
console.log(hello.charAt(2)); //l
charCodeAt – returns the numeric character code by index
const hello = "Hello, my name Alexander";
console.log(hello.charCodeAt(2)); //108
trim – removes spaces
The trim() method is used to remove spaces:
const hello = " Hello, my name Alexander ";
console.log(hello.trim()); //"Hello, my name Alexander"
Additionally, there are a number of methods that remove spaces from a specific side of a string:
- trimStart – removes a space from the beginning of a string
- trimEnd – removes a space from the end of a string
- trimLeft – removes a space from the left side of a string
- trimRight – removes a space from the right side of a string
concat – concatenates two strings
let hello = "Hello ";
let world = "world";
hello = hello.concat(world);
console.log(hello); // Hello world
Replacing a value in a string
replace – replaces the first match of one substring with another
The first parameter of the method specifies which substring to replace, and the second parameter to which substring to replace.
let hello = "Hello world";
goodbye = hello.replace("Hello", "Goodbye");
console.log(goodbye); //Goodbye world
replaceAll – replaces all matches of one substring with another
let carsonroad = "Bugatti, audi, Mercedes, Renault, Dacia. another Mercedes, BMW.";
carsonroad = carsonroad.replaceAll("Mercedes", "Mercedes-Benz");
console.log(carsonroad); //Bugatti, audi, Mercedes-Benz, Renault, Dacia. another Mercedes-Benz, BMW.
split – splits a string into an array at a certain separator
A string is used as a separator, which is passed as a parameter to the method.
Let’s look at an example:
const message = "Hello my dear friend!";
const messageParts = message.split(" ");//space character
console.log(messageParts); // ["Hello", "my", "dear", "friend"]
Checking the beginning and end of a string
startsWith – checks if a string starts with a substring
This method returns true if it starts or false if not.
const hello = "Hello my dear friend!";
console.log(hello.startsWith("Hello"));// true
console.log(hello.startsWith("Bye"));// false
endsWith – checks if a string ends with a substring
Returns true if the string ends with the specified substring.
const hello = "Hello my dear friend!";
console.log(hello.endsWith("friend!"));// true
console.log(hello.endsWith("dear"));// false
As the second parameter, you can pass the index of the second string from which the search begins:
console.log(hello.startsWith("Hello", 7));//false
Filling in a string
padStart – allows you to stretch the string on the left
The method will expand the string by a certain number of characters and fill the string on the left with spaces or given characters.
let hello = "hello".padStart(8);//8 characters in string
console.log(hello); // the method will add the missing 3 characters " hello"
As the second parameter, we can pass to the methods a value that needs to be added to the string instead of spaces:
let hello = "hello".padStart(17, "JavaScript, "); // "JavaScript, hello"
padEnd – allows you to stretch the line to the string
Similarly, padStart will expand the string by a certain number of characters and pad the string to the right with spaces or the given symbols.
let hello = "hello".padEnd(8);//8 characters in the string
console.log(hello); // method to add missing 3 characters "hello "