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JavaScript Basic String Functions

Here are some of the most fundamental JS string functions.

Assume the code below is declared at the top level in the following examples.

var string = "string"
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Changing the case


Converts a string to lowercase letters.

let s6 = "STRING".toLowerCase();
console.log(s6); //=> "string"
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Converts a string to uppercase letters.

let s7 = string.toUpperCase();
console.log(s7); //=> "STRING"
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Searching for a substring

indexOf(subst, pos)

It looks for the substr in a string, starting from the given position pos.

console.log(string.indexOf('i')) //=> 3

let string2 = 'string string'

console.log(string2.indexOf('string', 2)) //=> 7
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Checks whether a string contains the specified string/characters.

console.log(string.includes("s")); //=> true
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Searches a string for a match against a regular expression, and returns the matches.

const regex = /\w/g;
let s4 = string.match(regex);
console.log(s4); //=> ["s", "t", "r", "i", "n", "g"]
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Getting a substring


Extracts a part of a string and returns a new string.

let s2 = string.slice(0, 3); ///=> str
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Extracts a part of a string and returns a new string.

let s2 = string.substring(0, 3); ///=> str
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Transforming a string


Splits a string into an array of substrings.

let s1 = string.split("");
console.log(s1); //=> ["s", "t", "r", "i", "n", "g"]
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Joins two or more strings, and returns a new joined strings.

let s3 = string.concat("string");
console.log(s3); //=> stringstring
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Searches a string for a specified value, or a regular expression, and returns a new string where the specified values are replaced.

let s5 = string.replace(/s/, "S");
console.log(s5); //=> String
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Removes whitespace from both ends of a string.

let s8 = " strn g   ".trim();
console.log(s8); //=> strn g

let s9 = "  string  ".trimLeft();
console.log(s9); //=> "string  "

let s10 = "  string    ".trimRight();
console.log(s10); //=> "  string"
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Discussion (24)

aliciab13550469 profile image
Alicia Black

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elmadavis profile image

Is there any replace function used in Java? These mentioned methods or functions are useful. I need assignment writing help from any developer here I need to use these functions. Can we use them with individual data types like int, var, char rather than a string?

harrywilliams1 profile image

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Myprivate Mentor • Edited on

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