A detailed review of useful JS functions that will help you work with the
String data type.
String. It doesn’t matter if there’s 1 char or 10k lines, it’s still a
String. Before we get to the review of the built-in
String functions, take a note that the length of all JS strings is stored in the
length property. You can access it directly and don’t have to call any specific getter method.
const s = 'Hello, World!'; console.log(s.length);
The second important point, that deserves its own quote is
All strings in JS are immutable.
Once a string is created, it will never be changed. Functions like
slice, will always return a new string, but the original one will be left intact.
For demonstration purposes I’ll assume we have some string
s declared as a constant with the value
I am going to become a FULL STACK JS Dev with Coderslang. Further, I’ll list some ideas that we might want to apply to this string and ways to do this.
const s = 'I am going to become a FULL STACK JS Dev with Coderslang';
How to check if a string includes another string
To check if our string contains another string, we should use the
includes function. It will return
false based on the result of the check.
console.log(s.includes('FULL STACK')); // true console.log(s.includes('cheeseburger')); // false
Another way of doing this is by using the
lastIndexOf functions. Both of them will lookup if the string contains another string and returns the index of the beginning of the match. If no match is found, it means that the original string doesn’t include the search string and the result will be -1;
console.log(s.indexOf('AWS')); // -1 console.log(s.lastIndexOf('AWS')); // -1
The difference between
lastIndexOf becomes evident when there are multiple matches inside the string.
console.log(s.indexOf('g')); // 5 console.log(s.lastIndexOf('g')); // 55
indexOfstarts the lookup from the beginning
lastIndexOfstarts the lookup from the end
This determines the difference in the result.
In any case, we can use both
-1, then it does. Otherwise, it doesn’t.
How to determine if one string starts with another string
To check if a string starts with another string, there’s a
startsWith function. It returns
true if our string starts with another string or
false if it doesn’t.
console.log(s.startsWith('I am')); // true console.log(s.startsWith('You are')); // false
How to determine if one string ends with another string
To check if a string ends with another string, there’s an
endsWith function. It works almost the same way as
startsWith, but it checks the end of the string, not the start.
console.log(s.endsWith('Coderslang')); // true console.log(s.endsWith('Node.js')); // false
How to remove spaces at the beginning of the end of the string
To remove the whitespace at the start or the end of the string, you can use these functions:
trimStart- to remove spaces at the beginning of the string
trimEnd- to remove spaces at the end of the string
trim- to do both actions at once and remove leading and trailing whitespace
Our base string won’t suffice to demonstrate this example, so we’ll create another one.
const stringWithSpaces = ' I learn JS with Coderslang every day '; console.log(stringWithSpaces.trimStart()); //'I learn JS with Coderslang every day ' console.log(stringWithSpaces.trimEnd()); //' I learn JS with Coderslang every day' console.log(stringWithSpaces.trim()); //'I learn JS with Coderslang every day'
How to convert a string to the UPPERCASE or the lowercase
To change all characters of the string to the uppercase you can use the function
toUpperCase and for the lowercase, you can use
console.log(s.toUpperCase()); // I AM GOING TO BECOME A FULL STACK JS DEV WITH CODERSLANG console.log(s.toLowerCase()); // i am going to become a full stack js dev with coderslang
How to replace a character in a string with a different one
To replace a character with another one in JS, you can use the
replace function. Pass it two strings, and it will replace the first string with the second one.
console.log(s.replace(' ', '!')) // I!am going to become a FULL STACK JS Dev with Coderslang console.log(s.replace('I am', 'You are')) // You are going to become a FULL STACK JS Dev with Coderslang
You might be surprised with the result as
replace was applied only once. But that’s how it works in the base case.
If you want to change all occurrences of a substring, you should use the
console.log(s.replaceAll(' ', '!')) // I!am!going!to!become!a!FULL!STACK!JS!Dev!with!Coderslang
TypeError: s.replaceAll is not a function
If you do, then
replaceAll isn’t supported in your environment and you can either implement it yourself or use a regular expression with the
g flag. This will instruct
replace to be applied globally.
const regex = new RegExp(' ', 'g'); const s = 'I am going to become a FULL STACK JS Dev with Coderslang'; console.log(s.replace(regex, '!')); // I!am!going!to!become!a!FULL!STACK!JS!Dev!with!Coderslang
Regular expressions are a very powerful tool, so make sure to learn them if you haven’t already.
That concludes the review of the most useful built-in
String functions in
JS. Is there something else you want to add to this article or maybe request a new one?