Strings & String Methods

Usernames, search queries, file paths, JSON, URLs, messages — almost everything a program touches arrives as text . Mastering strings is mastering the most common job in real-world code: cleaning, slicing, searching, and reshaping words.

Learn Strings & String Methods in our free JavaScript course — a beginner-friendly interactive lesson with runnable examples, a practice exercise and a quick…

Part of the free JavaScript course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

This lesson is your reference for the string methods you'll reach for every single day.

🧵 Real-World Analogy: A string is like a row of beads on a thread:

You can write strings with single quotes, double quotes, or backticks. Backtick strings (template literals) are special: they interpolate expressions and span multiple lines.

The .length property counts characters. Index with brackets or, for negative-from-the-end access, the modern .at() method.

Checking whether text contains, starts with, or ends with something is one of the most common tasks in form validation, routing, and filtering:

slice(start, end) copies characters from start up to (but not including) end . Negative numbers count from the end, which makes "grab the last few characters" trivial:

Casing, trimming whitespace, replacing, and padding cover most "clean this input up" jobs. Remember: each returns a new string.

split turns a string into an array; join turns an array back into a string. Together they power CSV parsing, word counting, and reformatting:

These lines should take a raw filename and produce a clean uppercase extension. They are scrambled — reorder them so the final log is PDF .

Why: you need the raw string (B) before you can trim it (D). The dot position (A) must be found on the trimmed string, and slice(dot + 1) (C) depends on that index. Only then can you uppercase and print (E). Note: line A in the puzzle searched file but the fixed version searches trimmed — searching the untrimmed string would offset every index by the leading spaces.

hi — strings are immutable, so the bracket assignment is silently ignored. To capitalize you'd need s = "H" + s.slice(1) .

a+b-c — replace with a plain string only swaps the first match. Use replaceAll("-", "+") to get a+b+c .

2 — splitting on a single space produces ["hello", "world"] , an array of length 2. This is the classic word-count pattern.

Up next: Numbers & Math — precision, rounding, and the famous 0.1 + 0.2 surprise! 🔢

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