New String Methods

New String Methods

ES6 added several useful methods to the String prototype that replace clunky workarounds with clean, readable code.

startsWith()

const url = "https://example.com/api/users";

url.startsWith("https");        // true
url.startsWith("http://");      // false
url.startsWith("example", 8);   // true (start searching at index 8)

Replaces: url.indexOf("https") === 0

endsWith()

const file = "report.pdf";

file.endsWith(".pdf");    // true
file.endsWith(".doc");    // false
file.endsWith("port", 6); // true (check only first 6 characters: "report")

Replaces: file.indexOf(".pdf") === file.length - 4

includes()

const sentence = "The quick brown fox jumps over the lazy dog";

sentence.includes("fox");       // true
sentence.includes("cat");       // false
sentence.includes("quick", 5);  // false (starts searching at index 5)

Replaces: sentence.indexOf("fox") !== -1

repeat()

"ha".repeat(3);      // "hahaha"
"abc".repeat(0);     // ""
"=-".repeat(20);     // "=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-"

// Practical: padding
function padLeft(str, length, char = " ") {
    const padding = char.repeat(Math.max(0, length - str.length));
    return padding + str;
}

padLeft("42", 5, "0");  // "00042"

padStart() and padEnd() (ES2017)

// padStart — pad from the beginning
"42".padStart(5, "0");    // "00042"
"hi".padStart(10);        // "        hi"

// padEnd — pad from the end
"42".padEnd(5, "0");      // "42000"
"hi".padEnd(10, ".");     // "hi........"

// Practical: time formatting
const hours = "9";
const minutes = "5";
const time = `${hours.padStart(2, "0")}:${minutes.padStart(2, "0")}`;
// "09:05"

trimStart() and trimEnd() (ES2019)

const messy = "   hello   ";

messy.trim();       // "hello"       (both sides)
messy.trimStart();  // "hello   "    (left only)
messy.trimEnd();    // "   hello"    (right only)

All New String Methods

Method	What It Does	Returns
startsWith(str)	Checks if string starts with str	Boolean
endsWith(str)	Checks if string ends with str	Boolean
includes(str)	Checks if string contains str	Boolean
repeat(n)	Repeats string n times	String
padStart(len, char)	Pads start to reach len	String
padEnd(len, char)	Pads end to reach len	String
trimStart()	Removes leading whitespace	String
trimEnd()	Removes trailing whitespace	String

Practical Example: URL Validator

function isSecureUrl(url) {
    return url.startsWith("https://");
}

function isImageFile(filename) {
    return filename.endsWith(".jpg") || 
           filename.endsWith(".png") || 
           filename.endsWith(".gif");
}

function containsKeyword(text, keyword) {
    return text.toLowerCase().includes(keyword.toLowerCase());
}

isSecureUrl("https://example.com");  // true
isImageFile("photo.png");            // true
containsKeyword("Hello World", "world");  // true

Key Takeaways

• startsWith(), endsWith(), includes() replace indexOf checks
• repeat() creates repeated strings without loops
• padStart() / padEnd() are perfect for formatting numbers and alignment
• All methods are case-sensitive — use toLowerCase() for case-insensitive checks
• These methods return new strings — strings are immutable in JavaScript