Strings and template literals

Three ways to write a string

A string is a sequence of characters: letters, digits, spaces, emoji. You can write it with single quotes, double quotes or backticks. Single and double quotes work the same. Backticks make a template literal, which can hold placeholders and line breaks.

const city = 'Pune';
const state = "Maharashtra";
const line = `${city} is in ${state}`;
console.log(line);        // Pune is in Maharashtra
const address = `Flat 4B
MG Road`;
console.log(address);     // two lines

Inside a placeholder ${...} you can write any expression: `Total: ${price * qty}`. This is much easier to read than joining pieces with +.

Escape characters

A backslash starts an escape: \n is a new line, \t a tab, \' a quote inside single quotes, and \\ a real backslash. Windows file paths like C:\\Users need double backslashes inside normal strings.

Length and characters

const word = 'Namaste';
console.log(word.length);  // 7
console.log(word[0]);      // 'N'
console.log(word.at(-1));  // 'e' (at() accepts negative positions)
console.log(word[10]);     // undefined (no error)

Strings are immutable

Immutable means it cannot be changed. word[0] = 'n' silently does nothing. Every string method gives you a new string and leaves the original as it was. So you must store the result.

let name = '  asha  ';
name.trim();             // result thrown away!
console.log(name);       // '  asha  '
name = name.trim().toUpperCase();
console.log(name);       // 'ASHA'

The methods you will use every day

slice also accepts negative numbers: 'invoice.pdf'.slice(-3) is 'pdf'. replace changes only the first match unless you use replaceAll (or a regular expression with the g flag, module 7).

Comparing strings

=== compares strings exactly, including capital letters: 'Delhi' === 'delhi' is false. Compare in one case: a.toLowerCase() === b.toLowerCase(). < and > compare character codes, so 'Z' < 'a' is true. To sort names the way people expect, use a.localeCompare(b).