js var的值怎么使用

// 声明一个变量并赋值
var myVariable = "Hello, World!";

// 在函数内部声明变量
function myFunction() {
    var localVar = "I am local";
    console.log(localVar); // 输出: I am local
}

myFunction();
console.log(myVariable); // 输出: Hello, World!
console.log(localVar); // 报错: localVar is not defined

console.log(myVar); // 输出: undefined
var myVar = "Hello";

console.log(myVar); // 报错: myVar is not defined
let myVar = "Hello";

var globalVar = "I am global";

function myFunction() {
    var localVar = "I am local";
    console.log(globalVar); // 输出: I am global
}

myFunction();
console.log(localVar); // 报错: localVar is not defined

(function() {
    var privateVar = "I am private";
    console.log(privateVar); // 输出: I am private
})();

console.log(privateVar); // 报错: privateVar is not defined