This post is originally published to my blog.
In this post I will summarize 10 javascript string methods you should at least known according to me.
If interested read here 10 javascript array methods you should know
.
String is anything inside single or double quotes.
Here are 10 javascript string methods you should know.
1. startsWith()
Check if string starts with specified character(s).
const str = 'JavaScript is amazing';
console.log(str.startsWith('JavaScript')); // true
console.log(str.startsWith('Java')); // true
console.log(str.startsWith('javascript')); // false
// position is optional
// if not specified, the default value is 0
console.log(str.startsWith('Script', 4)); // true
console.log(str.startsWith('SCRIPT', 4)); // false
2. endsWith()
Check if string ends with specified character(s).
const str = 'JavaScript is amazing';
// check if ends with 'amazing'
console.log(str.endsWith('amazing')); // true
console.log(str.endsWith('ing')); // true
console.log(str.endsWith('Amazing')); // false
// length is optional
// if not specified, the default value is length of the string
console.log(str.endsWith('is', 13)); // true
console.log(str.endsWith('i', 13)); // false
console.log(str.endsWith('s', 13)); // true
3. includes()
Check if string contains specified character(s).
const str = 'JavaScript is amazing';
console.log(str.includes('Script')); // true
console.log(str.includes('script')); // false
console.log(str.includes(' ')); // true
console.log(str.includes('array')); // false
4. slice()
Copy some part of string without modifying the original one.
const str = 'JavaScript is amazing';
// Default start index is 0
console.log(str.slice()); // 'JavaScript is amazing'
// start copy at index 4
console.log(str.slice(4)); // 'Script is amazing'
// end copy at index 10(character at this index will not be included)
console.log(str.slice(0, 10)); // 'JavaScript'
5. toUpperCase()
Convert string into upper case.
const str = 'JavaScript is amazing';
console.log(str.toUpperCase()); // 'JAVASCRIPT IS AMAZING'
6. toLowerCase()
Convert string into lower case.
const str = 'JavaScript is amazing';
console.log(str.toLowerCase()); // 'javascript is amazing'
7. charAt()
Return character at specified position.
const str = 'JavaScript is amazing';
console.log(str.charAt()); // 'J'
console.log(str.charAt(11)); // 'i'
console.log(str.charAt(14)); // 'a'
console.log(str.charAt(110)); // ''
8. split()
Split string into array of substrings.
const str = 'JavaScript is amazing';
const strNew = 'JavaScript-is-amazing';
console.log(str.split()); // ["JavaScript is amazing"]
// Separator string used to determine where to make each split
console.log(str.split('S')); // ["Java", "cript is amazing"]
console.log(str.split('is')); // ["JavaScript ", " amazing"]
console.log(str.split(' ')); // ["JavaScript", "is", "amazing"]
console.log(strNew.split('-')); // ["JavaScript", "is", "amazing"]
9. replace()
Replaces specified value with another value in a string.
const str = 'JavaScript is amazing';
console.log(str.replace('JavaScript', 'Node.js')); // 'Node.js is amazing'
// replace() method is case sensitive
// replace will not work
console.log(str.replace('Javascript', 'Node.js')); // 'JavaScript is amazing'
// use regular expression for case insensitive
console.log(str.replace(/Javascript/i, 'Node.js')); // 'Node.js is amazing'
// replace() method replaces only the first match
console.log(str.replace('a', 'A')); // 'JAvaScript is amazing'
// to replace all matches, use regular expression
console.log(str.replace(/a/g, 'A')); // 'JAvAScript is AmAzing'
10. repeat()
Return new string with specified number of copies of existing string.
const str = 'JavaScript';
console.log(str.repeat(3)); // 'JavaScriptJavaScriptJavaScript'
console.log(str.repeat(1)); // 'JavaScript'
console.log(str.repeat(0)); // ''
Top comments (14)
repeat
exists? :oI've been doing
new Array(52).join('a');
to make a string of 52a
s, but I could have just used'a'.repeat(52)
... now I need to make a little commit to update that.The other day I even ranted about how nice Python's
'a' * 52
would have been.They are not same
Oops, you're right! Typo on my part :) For the sake of my E2E tests, I actually think
repeat
would be easier to read.Actually repeat is easy to read
If you want to make string of 52 a's with repeat is so easy
Array index starts from 0 which means it will print 52 times.
Yass, and since join acts as 'glue', using 'a' as glue for 52 nothings will print 'a' 51 times. Give it a try ;)
Great list of methods for Strings. I would just like to highlight that String.startsWith() and String.repeat() are ES2015+ String.endsWith() is ES6+, so polyfill accordingly to support edge cases.
Thanks, was wondering about that!
Hi, thanks for the update. What about substr() function. Is it necessary when slice() exist?
substr() is not part of the core JavaScript language and may be removed in the future. Use slice() or substring() instead
I'm not sure whether this one is deprecated or maybe I read that incorrectly...
Thanks for this!
Very useful, Thanks!
Can you tell me real world use case of reapeat() method? Idk why we need it 🤔
Thanks in advance!