Lesson

JS Strings

Q: How do I convert another type into a string?

Use String(value) because it safely converts null to "null" and undefined to "undefined" without throwing errors.

Q: Why does str.at(-1) beat str[str.length - 1] ?

str.at(-1) is shorter, reads from the end naturally, and avoids repeating the variable name.

10 min reading

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JavaScript Strings: Quotes, Immutability, and Indexing

A JavaScript string is an immutable sequence of UTF-16 characters used to represent text. You can create strings with single quotes ('...'), double quotes ("..."), or backticks (`...`).

Quotes, Escapes, and Immutability

Single and double quotes behave identically, so pick one style and stay consistent. Backticks create template literals that span multiple lines and embed expressions with ${...}.

Strings in JavaScript cannot be changed in place. Trying word[0] = "H" silently fails (or throws a TypeError in strict mode); you must create a new string instead.

Accessing Characters and Length

Read .length to count UTF-16 code units, or use .at(-1) (ES2022) to read the last character cleanly without writing str[str.length - 1].

const city = "Chattogram";
const quote = 'She said, "Code runs cleanly!"';
const multiLine = `City: ${city}
Length: ${city.length}`;

console.log("First char:", city[0]);
console.log("Last char:", city.at(-1));
console.log(quote);
console.log(multiLine);

Common Escape Sequences

: Inserts a newline character inside quoted strings.
: Inserts a horizontal tab space.
\\: Writes a literal backslash character, useful for Windows file paths.
\" or \': Escapes a matching quote inside the same quote style.

Common Mistakes to Avoid

Wrapping strings with new String("abc"): Calling new String() creates an object wrapper instead of a primitive string, which breaks === comparisons and slows code down.
Assuming .length counts visual emojis accurately: Complex emojis use two UTF-16 units, so "🚀".length is 2. Use [..."🚀"].length when counting visual characters.
Using + across long multi-line strings: Template literals with backticks handle multi-line text cleanly without manual escapes.