学ぶ Data Types and Basic Operations

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JavaScript stores different kinds of data using data types. The main ones are:

String: text;
Number: numeric values;
Boolean: true / false;
Null: intentional empty value;
Undefined: not assigned.


              12345678910111213
            
// Assigning different data types to variables

let userName = "Alice"; // string
let userAge = 30; // number
let isMember = true; // boolean
let middleName = null; // null
let address; // undefined

console.log(userName); // Output: Alice
console.log(userAge); // Output: 30
console.log(isMember); // Output: true
console.log(middleName); // Output: null
console.log(address); // Output: undefined

You can perform various basic operations with these data types. With numbers, you can use addition (+), subtraction (-), multiplication (*), and division (/).

With strings, the + operator is used for concatenation, meaning joining two or more strings together. JavaScript sometimes automatically converts one data type to another when performing operations—this is called type coercion. For example, adding a string and a number results in a string because JavaScript converts the number to a string.


              12345678910111213141516171819
            
// Basic operations

let a = 10;
let b = 5;
let sum = a + b; // Addition: 15
let difference = a - b; // Subtraction: 5

let greeting = "Hello, ";
let name = "Bob";
let welcomeMessage = greeting + name; // Concatenation: "Hello, Bob"

let result = "Age: " + 25; // Type coercion: "Age: 25"
let mixed = 5 + "5"; // Type coercion: "55"

console.log(sum); // Output: 15
console.log(difference); // Output: 5
console.log(welcomeMessage); // Output: Hello, Bob
console.log(result); // Output: Age: 25
console.log(mixed); // Output: 55

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セクション 1. 章 4

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