startsWith() checks whether a JavaScript string begins with a specific substring. It returns true or false and is case-sensitive.
Use it for prefix checks such as URL paths, file names, command strings, IDs, and user input validation.
Environment: Node.js v20.18.2. After each runnable snippet, the following paragraph states the expected console output (order and values).
Method 1: Check the Start of a String
console.log("starts-basic:", "JavaScript".startsWith("Java"));You should see one line logging starts-basic: true.
The string begins with Java, so the result is true.
Method 2: Use the Position Argument
console.log("starts-position:", "Hello JavaScript".startsWith("Java", 6));You should see one line logging starts-position: true.
The second argument tells JavaScript where to start checking.
Method 3: Remember Case Sensitivity
console.log("JavaScript".startsWith("java"));You should see one line logging false.
Convert both strings to the same case when you need a case-insensitive check.
Method 4: Case-Insensitive startsWith
const text = "JavaScript";
console.log(text.toLowerCase().startsWith("java"));You should see one line logging true.
This is useful for user-entered text.
Common Questions About startsWith in JavaScript
Is startsWith case-sensitive?
Yes. "JavaScript".startsWith("java") returns false.
What does startsWith return?
It returns a boolean: true if the string starts with the search text, otherwise false.
Can startsWith start checking from another position?
Yes. Pass the position as the second argument: str.startsWith(search, position).
Summary
Use startsWith() to check whether a JavaScript string begins with a specific substring. It is case-sensitive, supports an optional position argument, and returns a boolean, making it useful for validation, routing, prefixes, and file-name checks.
