🧵 Day 7 — Strings in JavaScript (Methods & Template Literals)

🔤 What is a String?

A string is a sequence of characters used to represent text.

jsCopyEditlet greeting = "Hello, world!";

Strings are immutable — you can create new strings from existing ones, but you can't change a character inside a string directly.

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✍️ Ways to create strings

jsCopyEditlet s1 = "Hello";
let s2 = 'World';
let s3 = `Template literal with ${s1} ${s2}`; // backticks

Template literals (backticks) let you embed expressions with ${...}, and support multi-line strings.

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🔧 Useful String Methods (with examples)

• length — number of characters

    jsCopyEdit"abc".length // 3
  

• charAt(index) / bracket notation

    jsCopyEditlet str = "JavaScript";
    str.charAt(0)   // "J"
    str[1]          // "a"
  

• toUpperCase() / toLowerCase()

    jsCopyEdit"hi".toUpperCase() // "HI"
  

• trim() — remove whitespace ends

    jsCopyEdit"  hello  ".trim() // "hello"
  

• indexOf(sub) / lastIndexOf(sub)

    jsCopyEdit"banana".indexOf("an") // 1
  

• includes(sub) — boolean

    jsCopyEdit"hello".includes("ll") // true
  

• slice(start, end) / substring(start, end)

    jsCopyEdit"JavaScript".slice(4, 10) // "Script"
  

• split(separator) — convert to array

    jsCopyEdit"a,b,c".split(",") // ["a","b","c"]
  

• replace(old, new) (first occurrence) and with regex for all

    jsCopyEdit"red blue red".replace("red", "green") // "green blue red"
  

• repeat(n) — repeat string

    jsCopyEdit"ha".repeat(3) // "hahaha"
  

• startsWith() / endsWith()

    jsCopyEdit"hello".startsWith("he") // true
  

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🧠 Template Literals (Backticks)

Template literals make string construction clearer and allow interpolation and newlines:

jsCopyEditlet name = "Gift";
let msg = `Hello ${name},
Welcome to Day 7!`;

They also support expressions:

jsCopyEdit`2 + 3 = ${2 + 3}` // "2 + 3 = 5"

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🧪 Day 7 Practice Problems (Easy → Hard)

1) 🟢 Easy — Access & Length

Given let city = "Lagos"; print the first character and the string length.

Solution

jsCopyEditlet city = "Lagos";
console.log(city[0]);        // "L"
console.log(city.length);    // 5

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2) 🟡 Intermediate — Capitalize Name

Write capitalize(name) that returns the name with the first letter uppercase and the rest lowercase. Example: "gIfT" → "Gift".

Solution

jsCopyEditfunction capitalize(name) {
  if (!name) return "";
  return name[0].toUpperCase() + name.slice(1).toLowerCase();
}

console.log(capitalize("gIfT")); // "Gift"

Explanation: slice(1) returns substring from index 1 to end; toLowerCase() normalizes the rest.

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3) 🔴 Hard — Reverse Words in a Sentence

Write reverseWords(sentence) that reverses the order of words (not characters).
Input: "I love JavaScript" → Output: "JavaScript love I"

Solution

jsCopyEditfunction reverseWords(sentence) {
  return sentence
    .trim()
    .split(/\s+/)     // split on one or more spaces
    .reverse()
    .join(" ");
}

console.log(reverseWords("I love JavaScript")); // "JavaScript love I"

Notes: trim() removes extra ends; split(/\s+/) handles multiple spaces robustly.

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✅ Recap

• Strings are immutable text values.

• Use template literals for interpolation and multi-line strings.

• Key methods: slice, split, replace, indexOf, includes, toUpperCase, trim.

• Practice manipulating strings and combining methods.