Check if String starts with Substring in JavaScript

Check if String starts with Substring #

To check if a string starts with a substring, call the startsWith() method on the string, passing it the substring as a parameter. The startsWith method returns true if the string starts with the substring, otherwise it returns false.

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const str = 'hello world';

if (str.startsWith('hello')) {
  // 👇️ this runs
  console.log('✅ string starts with hello');
} else {
  console.log('⛔️ string does NOT start with hello');
}

We used the String.startsWith method to determine if a string starts with a specific substring.

The method returns a boolean result:

• true if the string starts with the substring
• false if it doesn't

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const str = 'HELLO world';
const substr = 'hello';

if (str.toLowerCase().startsWith(substr.toLowerCase())) {
  // 👇️ this runs
  console.log('✅ string starts with hello');
} else {
  console.log('⛔️ string does NOT start with hello');
}

Check if String starts with Substring using indexOf #

To check if a string starts with a substring, call the indexOf() method on the string, passing it the substring as a parameter. If the indexOf method returns 0, then the string starts with the substring, otherwise it doesn't.

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// Supported in IE

const str = 'hello world';
const substr = 'hello';

if (str.indexOf('hello') === 0) {
  // 👇️ this runs
  console.log('✅ string starts with hello');
} else {
  console.log('⛔️ string does NOT start with hello');
}

The String.indexOf method returns the index of the first occurrence of a substring in a string.

If the substring is not contained in the string, it returns -1.

If the method returns 0, we can conclude that the string starts with the substring.

Check if String starts with Substring using Regex #

To check if a string starts with a substring, use the test() method with a regular expression that matches the substring in the beginning of the string. The test method will return true if the string starts with the substring and false otherwise.

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if (/^abc/.test('abc123')) {
  // 👇️ this runs
  console.log('✅ string starts with abc');
} else {
  console.log('⛔️ string does NOT start with abc');
}

We used the RegExp.test method to check if a string begins with a specific substring.

The method returns true if the regular expression is matched in the string and false otherwise.

The forward slashes / / mark the start and end of the regular expression.

The caret ^ matches the beginning of the input.

In this example, we check if the string abc123 starts with the substring abc.

If you ever need help reading a regular expression, bookmark this regex cheatsheet from MDN. It's by far the best one out there.

If you want to make the regular expression case insensitive, add the i flag.

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// 👇️ with `i` flag
if (/^abc/i.test('ABC123')) {
  // 👇️ this runs
  console.log('✅ string starts with abc');
} else {
  console.log('⛔️ string does NOT start with abc');
}

The i flag allows us to perform case insensitive search in the string.

Further Reading #

• Check if String ends with Substring in JavaScript
• Check if String contains Special Characters in JavaScript