String Methods
Built-in methods to transform and inspect strings.
Syntax
str.toUpperCase()
str.trim()
str.replace(a, b)Strings come with many built-in methods. A few essentials:
toUpperCase()/toLowerCase()— change case.trim()— remove whitespace from both ends.replace()— swap text.repeat()— repeat a string.
Example
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When to use it
- Normalise a user's email input to lowercase before comparing it against stored credentials.
- Trim whitespace from a form field value before validating its length.
- Replace placeholder tokens in an email template with the user's actual name and order details.
More examples
Trim and lowercase an email
Chains trim() and toLowerCase() to normalise an email address from user input.
const email = " [email protected] ";
const normalised = email.trim().toLowerCase();
console.log(normalised); // "[email protected]"includes startsWith endsWith
Uses startsWith, includes, and endsWith to inspect parts of a URL string.
const url = "https://api.example.com/users";
console.log(url.startsWith("https")); // true
console.log(url.includes("/users")); // true
console.log(url.endsWith(".json")); // falseReplace placeholder tokens
Uses replace() to substitute placeholder tokens in an email template with real values.
const tpl = "Hello {{name}}, your order {{id}} is ready.";
const msg = tpl.replace("{{name}}", "Alice").replace("{{id}}", "ORD-001");
console.log(msg);
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