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Examples

Compare Two Strings in JavaScript (7 Programs)

Comparing two strings in JavaScript is a common requirement in various applications, such as user authentication, sorting, and validation. Understanding the different methods to compare strings in JavaScript ensures accurate results, considering case sensitivity and encoding differences.

This guide explores multiple ways to compare two strings in JavaScript, helping developers choose the most suitable approach for their needs.

Compare Two Strings in JavaScript Using Equality Operators

The simplest way to compare strings is by using equality operators (== or ===).

Code

const str1 = "hello";
const str2 = "hello";
const str3 = "Hello";

console.log(str1 === str2);  // true
console.log(str1 === str3);  // false
console.log(str1 == str3);   // false

Output

true
false
false

Explanation

  • The === operator checks both value and type.

  • The == operator performs type coercion but is case-sensitive.

Compare Two Strings in JavaScript Using localeCompare() Method

The localeCompare() method provides a locale-sensitive string comparison.

Code

const str1 = "apple";
const str2 = "banana";

console.log(str1.localeCompare(str2));  // -1 (apple comes before banana)
console.log(str2.localeCompare(str1));  // 1  (banana comes after apple)
console.log(str1.localeCompare(str1));  // 0  (both are equal)

Output

-1
1
0

Explanation

  • Returns -1 if the first string comes before the second.

  • Returns 1 if the first string comes after the second.

  • Returns 0 if both strings are equal.

Case-Insensitive String Comparison in JavaScript

To perform a case-insensitive comparison, convert both strings to the same case before comparing.

Code

const str1 = "Hello";
const str2 = "hello";

console.log(str1.toLowerCase() === str2.toLowerCase());  // true

Output

true

Explanation

The toLowerCase() method converts both strings to lowercase before comparing them.

Comparing Two Strings in JavaScript Using toUpperCase()

Using toUpperCase() ensures both strings are converted to uppercase for comparison.

Code

const str1 = "Hello";
const str2 = "HELLO";

console.log(str1.toUpperCase() === str2.toUpperCase());  // true

Output

true

Explanation

The toUpperCase() method converts both strings to uppercase before comparison.

JS String Comparison Using Regular Expressions

Regular expressions can be used to compare strings flexibly.

Code

const str1 = "hello";
const str2 = "HELLO";
const regex = new RegExp(str1, "i");

console.log(regex.test(str2));  // true

Output

true

Explanation

The RegExp object with the i flag performs a case-insensitive comparison.

Compare Two Strings in JavaScript Using Lexicographic **

JavaScript compares strings lexicographically (based on Unicode values).

Code

console.log("apple" < "banana");   // true (lexicographically 'a' < 'b')
console.log("grape" > "apple");    // true ('g' > 'a')

Output

true
true

Explanation

The comparison is based on Unicode values of characters.

Character-by-Character String Comparison in JavaScript

To compare strings manually, loop through each character.

Code

function compareCharacterByCharacter(str1, str2) {
    if (str1.length !== str2.length) return false;
    for (let i = 0; i < str1.length; i++) {
        if (str1[i] !== str2[i]) return false;
    }
    return true;
}

console.log(compareCharacterByCharacter("test", "test"));  // true
console.log(compareCharacterByCharacter("test", "best"));  // false

Output

true
false

Explanation

  • The function checks each character individually.

Concepts Used in String Comparisons

Case Sensitivity

  • Strings in JavaScript are case-sensitive by default.

Unicode Value Comparison

  • Strings are compared based on their Unicode values.

Normalization

  • Using toLowerCase() or toUpperCase() ensures consistency during comparisons.

Equality vs. Lexicographic Comparison

  • Use equality operators for direct matching and localeCompare() for sorting.