你能给我解释一下为什么if / else语句不能正常工作吗？

if (x > 10) {
    console.log("x is greater than 10");
} else {
    console.log("x is less than or equal to 10");
}

if (x > 10)
    console.log("x is greater than 10");  // 缺少花括号
else
    console.log("x is less than or equal to 10");  // 缺少花括号

let x = 5;
if (x > 10) {
    console.log("x is greater than 10");
} else {
    console.log("x is less than or equal to 10");
}

let x = 15;
if (x > 20) {  // 条件始终为假
    console.log("x is greater than 20");
} else {
    console.log("x is less than or equal to 20");
}

let x;
if (x > 10) {  // x未初始化
    console.log("x is greater than 10");
} else {
    console.log("x is less than or equal to 10");
}

function checkValue() {
    let x = 5;
    if (x > 10) {
        let y = "greater";
        console.log(y);
    } else {
        console.log("x is less than or equal to 10");
    }
    console.log(y);  // y未定义
}

let x = 5;
if (x > 10) {
    console.log("x is greater than 10");
} else {
    console.log("x is less than or equal to 10");
}