JavaScript: Test whether a string starts with a specified string

JavaScript String: Exercise-46 with Solution

Starts With Substring

Write a JavaScript function to test whether a string starts with a specified string.

Test Data:
console.log(startsWith('js string exercises', 'js'));
true

Visual Presentation:

Sample Solution:

JavaScript Code:

 // Define a function called startsWith that takes two parameters: input (a string) and string (another string).
function startsWith(input, string) {
  // Check if the index of the second string within the first string is 0, indicating that the first string starts with the second string.
  return input.indexOf(string) === 0;
}
// Test the startsWith function by calling it with two strings and logging the result to the console.
console.log(startsWith('js string exercises', 'js'));

Output:

true

Explanation:

The above code defines a function named "startsWith()" that checks if a given input string starts with a specified substring. It takes two parameters: 'input', which is the string to be checked, and 'string', which is the substring to check for at the beginning of the input string. Inside the function, it uses the 'indexOf' method to determine the position of the substring within the input string.

If the substring is found at the beginning (position 0), the function returns 'true'; otherwise, it returns 'false'.

Finally, the code tests the "startsWith()" function with a sample input and logs the result to the console.

Flowchart:

Live Demo:

See the Pen JavaScript Test whether a string starts with a specified string-string-ex-46 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that checks if a string starts with a specified substring using slice() comparisons.
• Write a JavaScript function that uses the built-in startsWith() method if available, with a fallback for older browsers.
• Write a JavaScript function that validates both input strings and returns true only if the main string starts with the search string.
• Write a JavaScript function that handles edge cases when the search string is empty.

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