函数调用栈

function A(){
    console.log("A start")
    B();
    console.log("A end")
}

function B(){
    console.log("B start")
    C();
    console.log("B end")
}

function C(){
    console.log("C start")
    D();
    console.log("C end")
}

function D(){
    console.log("D start")
    console.log("D end")
}

// 函数调用栈
A();