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JavaScript

How to Search and Replace Strings in JavaScript

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Search

There are a few ways to search for strings in JavaScript. Strings has the startsWith , endsWith , indexOf , lastIndexOf , charAt , search and includes , and match functions.

startsWith

startsWith checks if a string starts with the substring you pass in.

For example:

const str = "Hello world.";  
const hasHello = str.startsWith("Hello"); // trueconst str2 = "Hello world.";  
const hasHello2 = str.startsWith("abc"); // false

endsWith

endsWith checks if a string ends with the substring you pass in.

For example:

const str = "Hello world.";  
const hasHello = str.endsWith("world."); // trueconst str2 = "Hello world.";  
const hasHello2 = str.endsWith("abc"); // false

indexOf

indexOf finds the index of the first occurrence of the substring. Returns -1 if not found.

For example:

const str = "Hello Hello.";  
const hasHello = str.indexOf("Hello"); // 0  
const hasHello2 = str.indexOf("abc"); // -1

lastIndexOf

lastIndexOf finds the index of the last occurrence of the substring. Returns -1 if not found.

For example:

const str = "Hello Hello.";  
const hasHello = str.lastIndexOf("Hello"); // 6  
const hasHello2 = str.lastIndexOf("abc"); // -1

charAt

charAt returns the character located at the index of the string.

For example:

const str = "Hello";  
const res = str.charAt(0); // 'H'

search

search get the position of the substring passed into the function. It returns -1 if the substring is not found in the string.

Example:

const str = "Hello";  
const res = str.search('H'); // 0

includes

includes checks if the substring passed in is in the string. Returns true if it is in the string, false otherwise.

const str = "Hello";  
const hasH = str.includes('H'); // true  
const hasW = str.includes('W'); // false

Replace

The replace() function included with strings are useful for replacing parts of strings with another. It returns a new string with the string after substring is replace.

Example:

const str = "Hello Bob";  
const res = str.replace("Bob", "James"); // 'Hello James'

replace() can also be used to replace all occurrences of a substring, for example:

const str = "There are 2 chickens in fridge. I will eat chickens today.";  
const res = str.replace(/chickens/g, "ducks"); // "There are 2 chickens in fridge. I will eat chickens today."

If the first argument is a regular expression which searches globally, then it will replace all occurrences of the substring.

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