JavaScript "if X“then条件内容替换

if (条件) {
    // 条件为真时执行的代码
}

let x = 10;
if (x) { // 正确，x 已定义
    console.log('x is defined');
}

if (y) { // 错误，y 未定义
    console.log('y is defined');
}

let x = 0;
if (x == false) { // true，因为 0 被转换为 false
    console.log('x is false');
}

if (x === false) { // false，因为 0 不等于 false
    console.log('x is false');
}

// 简单的 if 语句
let age = 18;
if (age >= 18) {
    console.log('You are an adult.');
}

// if...else 语句
let hasLicense = true;
if (hasLicense) {
    console.log('You can drive.');
} else {
    console.log('You cannot drive.');
}

// if...else if...else 语句
let day = 'Monday';
if (day === 'Saturday' || day === 'Sunday') {
    console.log('It is the weekend.');
} else if (day === 'Monday') {
    console.log('It is the start of the week.');
} else {
    console.log('It is a weekday.');
}