Frugence Fidel

Posted on Jul 12, 2018 • Edited on Jul 15, 2022

10 JavaScript string methods you should know

#javascript #beginners #webdev

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)

ItsASine (Kayla) • Jul 13 '18

repeat exists? :o

I've been doing new Array(52).join('a'); to make a string of 52 as, 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.

Frugence Fidel • Jul 13 '18 • Edited

They are not same

 const first = new Array(2).join('a');
 console.log(first); // 'a'

 const second = 'a'.repeat(2);
 console.log(second); // 'aa'

 // new Array(52).join('a') will not print 52 a's, print 51 a's
 const aLength = new Array(52).join('a').length;
 console.log(aLength); // 51

ItsASine (Kayla) • Jul 13 '18 • Edited

Oops, you're right! Typo on my part :) For the sake of my E2E tests, I actually think repeat would be easier to read.

it('displays an error for too many characters', function() {
    relevantPage.middleInitial.sendKeys('a'.repeat(2)); // clearly shows that 2 is considered too many

    expect(relevantPage.middleInitialTooLongMessage.getText()).toEqual('Middle initial is too long');
});

Frugence Fidel • Jul 14 '18

Actually repeat is easy to read

If you want to make string of 52 a's with repeat is so easy

  const a = 'a'.repeat(52);
  console.log(a); // "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
  console.log(a.length); // 52

siddharthray • Jul 28 '18

Array index starts from 0 which means it will print 52 times.

diek • Jan 25 '19

Yass, and since join acts as 'glue', using 'a' as glue for 52 nothings will print 'a' 51 times. Give it a try ;)

Patrick Cole • Jul 20 '18

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.