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When Foo is not called

window.getName = function(){
    console.log(4);
}

When calling Foo()

getName = function(){
                console.log(1);
            };
// 相當(dāng)于更改了 window.getName

After the call, return this in Foo does point to window, so the final result is 1.

function Foo(){
    getName = function(){
        console.log(1);
    };
    return this;
}
//全局聲明一個(gè)變量getName
var getName = function (){ 
    console.log(4)
};
//重新賦值
getName = function () {
    console.log(1)
}
//最終打印結(jié)果為1
window.getName()

Foo().getName(); executes getName in Foo

function Foo(){
    getName = function(){
        console.log(1);
    };
    return this;
}

var getName = function (){ 
    console.log(4)
};

Foo().getName();

function Foo(){
    getName = function(){
        console.log(1);
    };
    return this;
}

var getName = function (){ 
    console.log(4)
};

getName = function () {
    console.log(1)
}

window.getName()

Check console.log(Foo()), are you sure it is window?

The getName in the Foo function is not declared with var, so it is global, so when Foo is run, the getName function inside the function will overwrite the one defined outside