Check if String Doesn't include Substring in JavaScript

Check if String Doesn't include Substring #

To check if a string doesn't include a substring, use the logical NOT (!) operator to negate the call to the includes() method. The NOT (!) operator returns false when called on a true value and vice versa.

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const str = 'hello world';

if (!str.includes('bye')) {
  console.log('✅ string does not include substring');
} else {
  console.log('⛔️ string includes substring');
}

We used the logical NOT (!) operator to negate the call to the String.includes method.

In the example, we check if the value bye is contained in the string hello world.

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const str = 'hello world';

console.log(str.includes('bye')); // 👉️ false

console.log(!str.includes('bye')); // 👉️ true

If we use the includes method without the logical NOT (!) operator, it returns true if the value is contained in the string and false otherwise.

Here are some more examples of using the logical NOT (!) operator.

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console.log(!true); // 👉️ false
console.log(!false); // 👉️ true

console.log(!'hello'); // 👉️ false
console.log(!''); // 👉️ true
console.log(!null); // 👉️ true

You can imagine that the logical NOT (!) operator first converts the value to a boolean and then flips the value.

Falsy values are: null, undefined, empty string, NaN, 0 and false.

Check if String Doesn't include Substring with indexOf #

To check if a string doesn't include a substring, call to the indexOf() method on the string, passing it the substring as a parameter. If the indexOf method returns -1, then the substring is not contained in the string.

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// Supported in IE

const str = 'hello world';

if (str.indexOf('bye') === -1) {
  console.log('✅ string does not include substring');
} else {
  console.log('⛔️ string includes substring');
}

The String.indexOf method returns the index of the first occurrence of a value in a string. If the value is not contained in the string, the method returns -1.

If the condition is met and the if block runs, we can be sure that the provided value is not contained in the string.

Further Reading #

• Check if an Object Property is Undefined in JavaScript
• Check if String is a Positive Integer in JavaScript