Strings are one of the most frequently used data types in JavaScript, yet many developers rely heavily on built-in methods without truly understanding how they work under the hood. If you're preparing for interviews, this is a gap worth fixing. JavaScript strings look simple, but behind methods like split(), trim(), includes(), and replace() is logic every developer should understand. What string methods are JavaScript provides built-in methods to manipulate strings: toUpperCase() Converts all characters in a string to uppercase. let str = " hello world " ; console . log ( str . toUpperCase ()); Enter fullscreen mode Exit fullscreen mode // "HELLO WORLD" toLowerCase() Converts all characters to lowercase. let str = " HELLO " ; console . log ( str . toLowerCase ()); // "hello" Enter fullscreen mode Exit fullscreen mode trim() Removes whitespace from both the beginning and end of a string. let str = " hello " ; console . log ( str .…