🚀 26 Built-in String Methods | JavaScript
Niall Maher
Posted on June 6, 2020
You can watch the video version here or keep scrolling for the code snippets.
⏰ There is links in the video description for all the timestamps so you can jump to the parts you like. 💜
🔗 All the titles are links to the MDN docs.
charAt
Returns the character at the specified index.
"Hello World".charAt(2); // returns "l"
// If we pass no value it defaults to an index of 0
"Hello World".charAt(); // returns "H"
// If we add an index that is undefined we get an empty string
"Hello World".charAt(20); // returns ""
charCodeAt
Returns the unicode of the character at the specified index.
"Hello world".charCodeAt(2); // returns 72 for "l"
// If we pass no value it defaults to an index of 0
"Hello world".charCodeAt(); // returns 108 for "H"
concat
Joins two or more strings, and returns a single concatenated string.
It's very similar to using the + operator on strings.
"Hello".concat(" world"); // returns "Hello world"
// With multiple strings
"Hello".concat(" world", " and", " other", " planets"); // returns "Hello world and other planets"
endsWith
Checks whether a string ends with specified string. We can add an optional second parameter with a limit to the string.
"Dogs are the best!".endsWith('best'); // returns false
"Dogs are the best!".endsWith('best!'); // returns true
// With second parameter for ending index
"Dogs are the best!".endsWith('best', 17); // returns true (because we picked the end of the string is at index 17)
fromCharCode
Converts Unicode values to readable characters.
fromCharCode is one of the few static methods available on the String Object. All the other ones we have been using have been what is known as an instance property. We access it by using the String keyword.
String.fromCharCode(67); // returns "C"
// Using multiple characters
String.fromCharCode(67, 111, 100, 250); // returns "Codú"
includes
Checks whether a string contains a specific string.
"Dogs are the best!".includes("Dogs") // returns true
// With optional starting index
"Dogs are the best!".includes("Dogs", 1) // returns false
"Dogs are the best!".includes("ogs", 1) // returns true
indexOf
Returns the position of the first found occurrence of a specified value in a string.
"test one two test".indexOf("test") // returns 0
"test one two test".indexOf("x") // returns -1
// With optional starting index
"test one two test".indexOf("test", 1) // returns 13
lastIndexOf
Returns the position of the last found occurrence of a specified value in a string.
"test one two test".lastIndexOf("test") // returns 13
// With optional limit because search starts from index 12.
"test one two test".lastIndexOf("test", 12) // returns 0
match
The match() method retrieves the result of matching a string against a regular expression or string.
// returns the first match
"This is the BEST".match("i"); // returns a regex iterator like this ["i", index: 2, input: "This is the BEST", groups: undefined]
// With a regex looking for uppercase characters
"This is the BEST".match(/[A-Z]/); // returns a regex iterator like this ["T", index: 0, input: "This is the BEST", groups: undefined]
// you can get all the matches without the details if you use a global regular expression
"This is the BEST".match(/[A-Z]/g); // returns [ 'T', 'B', 'E', 'S', 'T' ]
matchAll
A new feature in ES2020 so check your browser compatibility. matchAll is like the match method on steroids. It returns an RegExpStringIterator for the matches.
// Working with with the RegExpStringIterator can become easy to work with if we spread it into an array.
const matches = [..."This is the BEST".matchAll(/[A-Z]/g)];
matches.forEach(element => console.log(element));
/*
console.logs
[ 'T', index: 0, input: 'This is the BEST', groups: undefined ]
[ 'B', index: 12, input: 'This is the BEST', groups: undefined ]
[ 'E', index: 13, input: 'This is the BEST', groups: undefined ]
[ 'S', index: 14, input: 'This is the BEST', groups: undefined ]
[ 'T', index: 15, input: 'This is the BEST', groups: undefined ] */
For more information on working with the iterators check out the docs.
normalize
We can normalize a unicode string with normalize, what does that mean? Basically that we can see it in human readable form.
"\u0043\u006f\u0064\u00fa".normalize(); // returns "Codú"
padEnd
We can add "padding" to the end of a string so it equals a certain length. We pad it with whitespace by default but can choose replacement characters too.
// Entire length is 10 after padding
"Hello".padEnd(10); // returns "Hello "
// Entire length is 10 after padding with characters too
"Hello".padEnd(10, "*"); // returns "Hello*****"
padStart
We can add "padding" to the start of a string so it equals a certain length. We pad it with whitespace by default but can choose replacement characters too.
// Entire length is 10 after padding
"Hello".padStart(10); // returns " Hello"
// Entire length is 10 after padding with characters too
"Hello".padStart(10, "*"); // returns "*****Hello"
These padding might seem irrelevant but there was a case where a popular library that was pulled from npm that did this was pulled and basically broke the internet. You can google the left-pad incident for information on that.
repeat
Takes a number as an argument and repeats the string as many times as specified and returns as a single string.
"Hello".repeat(3); // returns "HelloHelloHello".
replace
Searches a string for a specified value, or a regular expression, and returns a new string where the specified value(s) are replaced. We can replace these values with a string or pass a function to operate on the match. Unless we pass a global regex it will only replace the first found occurance.
"cat, cat, cat".replace(/cat/, 'dog'); // returns "dog, cat, cat"
"cat, cat, cat".replace(/cat/g, 'dog'); // returns "dog, dog, dog"
"cat, cat, cat".replace("cat", 'dog'); // returns "dog, cat, cat"
"cat, cat, cat, bird".replace("cat", (i) => i + "dog"); // returns "catdog, cat, cat, bird"
replaceAll
We can use a regex or string to replace all instances of a string. We can replace these values with a string or pass a function to operate on the match. When working with global regex's there is not much difference between replace and replaceAll. Replace all only takes global regexs but if you pass it a string it will automatically replace all instances of that string. The second param can be a string to replace each instance or a function to operate on each instance.
"cat, cat, cat, bird".replaceAll(/cat/g, 'dog'); // returns "dog, dog, dog, bird"
"cat, cat, cat, bird".replaceAll("cat", 'dog'); // returns "dog, dog, dog, bird"
// With a function
"cat, cat, cat, bird".replaceAll("cat", (i) => i + "dog"); // returns "catdog, catdog, catdog, bird"
search
Searches a string for a specified value, or regular expression, and returns the starting position of the match.
"cat, dog, cat".search("dog"); // returns 5
// With a regex
"cat, dog, cat".search(/dog/g); // returns 5
slice
Extracts a part of a string and returns a new string.
"This is a string I want to slice".slice(27); // returns 'slice'
"This is a string I want to slice".slice(27, 28); // returns 's'
// And we can work backwards with negative values such as
"This is a string I want to slice".slice(-5); // returns "slice"
"This is a string I want to slice".slice(-5, -1); // returns "slic"
split
Splits a string into an array of substrings. We can give an optional limit as a second parameter.
// For all characters to be split give an empty string
"Hello darkness".split(""); // returns ["H", "e", "l", "l", "o", " ", "d", "a", "r", "k", "n", "e", "s", "s"]
// To split at spaces
"Hello darkness my old friend".split(" "); // returns ["Hello", "darkness", "my", "old", "friend"]
To limit the return length we can use an optional second parameter
"Hello darkness my old friend".split(" ", 2); // returns ["Hello", "darkness"]
startsWith
Checks, whether a string begins with specified characters and returns a boolean. We can give it an optional starting index as a second parameter.
"Hello".startsWith("h"); // true
"Hello".startsWith("e"); // false
// With optional starting index
"Hello".startsWith("e", 1); // true
substring
Extracts the characters from a string, between two specified indices. The second parameter is optional.
"Hello".substring(1, 4); // "ell"
// If we give no second parameter it will pick assume you have no end index.
"Hello".substring(1); // returns "ello"
toLowerCase
Converts a string to lowercase letters
"HeLlO wOrLd".toLowerCase(); // returns "hello world"
toUpperCase
Converts a string to uppercase letters.
"Hello world".toUpperCase(); // returns "HELLO WORLD"
trim
Removes whitespace from both ends of a string.
" Hello world ".trim(); // returns "Hello world"
trimEnd
Trims whitespace from the end
" Hello world ".trim(); // returns " Hello world"
trimStart
Trims whitespace from the start of a string.
" Hello world ".trim(); // returns "Hello world "
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Posted on June 6, 2020
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