Strings

Strings are JavaScript text

A string is a value that stores text: a name, a message, a file path, a button label, or the answer that prompt gives back. Strings are primitives, like you saw in the Data types lesson, which means the value itself is simple and immutable.

You have already seen JavaScript do something surprising with strings: "5" + 3 becomes "53" in Why JavaScript?. This lesson slows down and explains the text side of that rule before the Type conversion lesson gives the full conversion table.

We will cover quotes and template literals, escape sequences, length and indexing, immutability, and concatenation in that order. Later lessons named String methods, Template literals & tagged templates, Unicode & string internals, and Comparing & sorting text go deeper.

JavaScript gives you three common ways to write string literals. Single quotes and double quotes are the same kind of string; choose whichever makes the text easier to read. Backticks create a template literal, which can span lines and fill blanks with $${expression}.

In this replay, line 5 uses a template literal and line 6 uses old-fashioned concatenation. Change the person and predict whether the two printed lines still match.

1const name = "Ada";Run2const age = 12;3const single = 'A string can use single quotes.';4const double = "Double quotes make apostrophes easy: I'm learning.";5const template = `Hi, ${name}. Next year you will be ${age + 1}.`;6const same = "Hi, " + name + ". Next year you will be " + (age + 1) + ".";7console.log(template);8console.log(same);

Backticks are often clearer for sentences because the variable names sit where the values appear. Concatenation is still useful for short pieces and for gradually building a string.

An escape sequence is a backslash code inside a string. It says, “Do not read the next character normally.” For example, \n means put a line break here, and \" means include a quote mark instead of ending the string.

1console.log("Line 1\nLine 2");Run2console.log("Name\tScore");3console.log("She said \"hi\"");4console.log("C:\\notes");5console.log("Smile: \u{1F600}");

Use escapes when they make the string easier to write. If escaping gets noisy, switch quote styles or use a template literal. For example, "It's ok" is easier than 'It\'s ok'.

Strings are ordered. text.length tells you how many string positions there are. Bracket indexing reads one position: text[0] is the first position, and text[text.length - 1] is the last position when the string is not empty.

1const text = "JavaScript";2console.log(text.length);3console.log(text[0]);4console.log(text.at(-1));5console.log(text[99]);

If you ask for a position that does not exist, JavaScript gives undefined. That is the same “no value here” word you will study in the next lesson, Booleans, null & undefined.

Strings are primitive values, and primitive strings are immutable: you cannot edit one character in place. A variable can point to a different string later, but the original string value does not get patched.

Here is the tempting but wrong edit in a classic sloppy script:

1let word = "cat";2word[0] = "b";3console.log(word);

It prints cat. In strict mode, including JavaScript modules and code that starts with "use strict", the same assignment throws a TypeError instead of being silently ignored:

1"use strict";2let word = "cat";3word[0] = "b";4console.log(word);

1let word = "cat";Run2word = "b" + word.slice(1);3console.log(word);

Concatenation means joining strings. The + operator joins when either side is a string. += is the “join onto the existing value” shortcut, common in small loops.

1let message = "";Run2for (let i = 1; i <= 3; i = i + 1) {3  message += "#" + i + " ";4}5console.log(message);6console.log("Total: " + 2 + 3);7console.log("Total: " + (2 + 3));

The most important beginner trap is order. "Total: " + 2 + 3 starts with a string, so it joins left to right and produces "Total: 23". Add parentheses when you mean math first: "Total: " + (2 + 3).

Where you’ll use this

Strings show up whenever code talks to humans or other systems. You will use them to build labels, read form input, create URLs, print debug messages, and combine values in UI text.

1const user = "Ada";2const unread = 3;3const label = `${user} (${unread} new messages)`;4console.log(label);5 6const path = "/users/" + user;7console.log(path);

Notice the split: template literals read like sentences, while + is fine for short mechanical pieces like a URL path. When values come from prompt, remember the result is already a string.

Common misconceptions

Key takeaways

• Strings store text and are written with single quotes, double quotes, or backticks.
• Template literals use $${...} to insert expression results.
• Escape sequences such as \n, \t, and \" put special characters inside strings.
• length counts string positions, indexes start at 0, and missing indexes read as undefined.
• Strings are immutable; make a new string and reassign the variable when text needs to change.
• + and += concatenate strings; use parentheses when you need math first.

Up next: Booleans & truthiness, then undefined and null.