- Basic Use
- Find Many String
- How To Set Case Insensitive
- Find All Capital Letters
- How To Find Digits In A String
- Using Replace Function
- Using Search And Exec Function
- Use of test function
- Give Me Coffee
In JavaScript, a Regular Expression (RegEx) is an object that describes a sequence of characters used for defining a search pattern.
This post will go over some basic stuff about regular expressions. Regular Expressions enable us to easily find patterns in a string.
basic use - Let us find the word 'apple' in the string
const text = "This is an apple"; const regex = /apple/; const result = text.match(regex) console.log(result) /** output: [ 0: "apple" groups: undefined index: 11 input: "this is an apple" length: 1 ] */ Find Many String
We are going to use the previous example and were going to add a global option to the regex. This will create an array of all occurrences. Note, this is case sensitive.
Using match
const text = 'this is an apple and another apple or APPLe'; const regex = /apple/g; console.log(text.match(regex)); /** Output: ['apple', 'apple'] */ Using matchAll
const text = 'this is an apple and another apple or APPLe'; const regex = /apple/g; console.log([...text.match(regex)]); /** Output: [ 0: ['apple', index: 11, input: 'this is an apple and another apple or APPLe', groups: undefined] 1: ['apple', index: 29, input: 'this is an apple and another apple or APPLe', groups: undefined] ] */ How to Set Case Insensitive
We are going to add the i option to the modifier to make the pattern case insensitive.
const text = 'this is an apple and another apple or APPLe'; const regex = /apple/gi; console.log([...text.matchAll(regex)]) /** [ 0: ['apple', index: 11, input: 'this is an apple and another apple or APPLe', groups: undefined] 1: ['apple', index: 29, input: 'this is an apple and another apple or APPLe', groups: undefined] 2: ['APPLe', index: 38, input: 'this is an apple and another apple or APPLe', groups: undefined] ] */ Find All Capital Letters
const text = 'Make Arnold Reverse the Video about Eternal Latency'; const regex = /[A-Z]/g; // we still need to use the global option console.log(text.match(regex)) /** Output: ['M', 'A', 'R', 'V', 'E', 'L'] */ We can also set our regex to ignore the letter M.
const text = 'Make Arnold Reverse the Video about Eternal Latency'; const regex = /(?![M])[A-Z]/g; console.log(text.match(regex)); /** Output: ['A', 'R', 'V', 'E', 'L'] */ How To Find Digits in a string
const text = 'We have a sugar of 200g, a lemon of 1kg and 1000kg of water.'; const regex = /\d/g; // using \d to match any digit console.log(text.match(regex)); /** Output: ['2', '0', '0', '1', '1', '0', '0', '0'] */ Get FULL numbers by using the + option.
const text = 'We have a sugar of 200g, a lemon of 1kg and 1000kg of water.'; const regex = /\d+/g; // using \d+ find full number console.log(text.match(regex)); /** Output: ['200', '1', '1000'] */ Using Replace Function
We're going to find and replace an item. In this example, we're going to find capital letters and replace them with @.
const text = 'I have 1 item.'; const regex = /\d/g; // using \d+ find full number console.log(text.replace(regex, '@')); /** Output: I have @ item. */ Other samples:
// replace all capital letters const result = "This is A New Item".replace(/[A-Z]/g, '@'); console.log(result); // @his is @ @ew @tem // replace full numbers const result = "This is A 200kg New Item with 0% capacity".replace(/\d+/g, '@'); console.log(result); // This is A @kg New Item with @% capacity // replace all letter a const result = "This is A 200kg New Item with 0% capacity".replace(/[a]/gi, '@'); console.log(result); // This is @ 200kg New Item with 0% c@p@city Using Search and Exec function
Search will give us the index position of the first match.
const result = "We are the World".search(/the/g); console.log(result); // 7 Exec on the other hand is like a match but with the purpose to be used in a loop. returns an array of captures or null.
const text = "We are the people of the world"; const regex = /the/g; let arr; while ((arr = regex.exec(text)) !== null) { console.log(`Found ${arr[0]} in index ${arr.index}.`) } /** Output: Found the in index 7. Found the in index 21. */ Use of test function
The test Returns a Boolean value that indicates whether or not a pattern exists in a searched string.
example validating an email address(This is a complicated regex but the main point here is how to use the test function):
const regex = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/; console.log(regex.test('brojenuel@123.890')); // false console.log(regex.test('jenuelganawed936@gmail.com')); // true other example:
const text = "This is just a text"; console.log(/a/.test(text)); // true - because a exist on the text console.log(/\d/.test(text)); // false - because no digits found console.log(/[A-Z]/.test(text)); // true - because theres a capital letter console.log(/A/i.test(text)); // true - because letter a/A exist on the text Give Me Coffee
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