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Check if a String contains a Substring in JavaScript

Title : Check if a String contains a Substring in JavaScript

1. Check if a String contains a Substring with String.includes(): 

const str1 = "Hello, world!";
const substring1 = "world";

const containsSubstring1 = str1.includes(substring1);
console.log(containsSubstring1); // Output: true
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Explanation:

  • We use the includes() method on the string str1 to check if it contains the substring "world".
  • Since "world" is a part of "Hello, world!", includes() returns true.

2. Check if String Doesn't contain a Substring in JavaScript: 

const str2 = "Hello, world!";
const substring2 = "foo";

const doesNotContainSubstring2 = !str2.includes(substring2);
console.log(doesNotContainSubstring2); // Output: true
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Explanation:

  • We use the includes() method to check if the string str2 contains the substring "foo".
  • Since "foo" is not a part of "Hello, world!", includes() returns false.
  • Using the logical NOT (!) operator, we negate the result, which gives us true.

3. Check if a String contains a Substring with String.indexOf(): 

const str3 = "Hello, world!";
const substring3 = "world";

const containsSubstring3 = str3.indexOf(substring3) !== -1;
console.log(containsSubstring3); // Output: true
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Explanation:

  • We use the indexOf() method on the string str3 to check if it contains the substring "world".
  • indexOf() returns the index of the substring in the string if found, otherwise -1.
  • Since the substring "world" is found in "Hello, world!" at index position 7, indexOf() doesn't return -1, so the condition evaluates to true.

4. Check if String Doesn't contain a Substring using indexOf(): 

const str4 = "Hello, world!";
const substring4 = "foo";

const doesNotContainSubstring4 = str4.indexOf(substring4) === -1;
console.log(doesNotContainSubstring4); // Output: true
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Explanation:

  • We use the indexOf() method to get the index of the substring "foo" in the string str4.
  • Since "foo" is not a part of "Hello, world!", indexOf() returns -1.
  • We check if the returned value is equal to -1 to determine if the string doesn't contain the substring, which evaluates to true.

5. Using includes() and indexOf() with case sensitivity: 

const str5 = "Hello, world!";
const substring5 = "WORLD";

const containsSubstringCaseSensitive = str5.includes(substring5);
console.log(containsSubstringCaseSensitive); // Output: false

const containsSubstringIgnoreCase = str5.toLowerCase().includes(substring5.toLowerCase());
console.log(containsSubstringIgnoreCase); // Output: true
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Explanation:

  • By default, both includes() and indexOf() are case-sensitive.
  • In the first example, "WORLD" is not found in "Hello, world!" because of the different case, so includes() returns false.
  • In the second example, we convert both the string and the substring to lowercase before checking, so "world" is found in "hello, world!", and includes() returns true.

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