学ぶ Working with Strings and Numbers

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Strings in JavaScript are sequences of characters that you can combine, manipulate, and analyze. You can join strings together using the plus (+) operator, which is called concatenation.

Template literals, enclosed by backticks (`), allow you to insert variables directly into a string using ${}. String methods like length and toUpperCase help you measure and manipulate string values.


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// String concatenation
let firstName = "Ada";
let lastName = "Lovelace";
let fullName = firstName + " " + lastName; // "Ada Lovelace"
console.log(fullName);

// Template literals
let age = 30;
let greeting = `Hello, my name is ${fullName} and I am ${age} years old.`;
console.log(greeting);

// Common string methods
let shout = fullName.toUpperCase(); // "ADA LOVELACE"
console.log(shout);

let nameLength = fullName.length; // 12
console.log(nameLength);

Numbers in JavaScript are used for calculations and mathematical operations.

You can perform arithmetic using operators such as +, -, *, and /. The increment (++) and decrement (--) operators add or subtract one from a variable. Sometimes, you need to convert a string to a number for calculations.

JavaScript provides functions like parseInt for whole numbers and parseFloat for decimal numbers to help you convert string values into numbers.


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// Parsing and converting strings to numbers
let input = "42";
let parsedInt = parseInt(input); // 42 (number)
console.log(parsedInt);

let price = "19.99";
let parsedFloat = parseFloat(price); // 19.99 (number)
console.log(parsedFloat);

// Converting numbers back to strings
let num = 100;
let numAsString = num.toString(); // "100"
console.log(numAsString);

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セクション 1. 章 5

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セクション 1. 章 5