我的理解是，这实际上很简单：

• Javascript总是按值传递，但是当变量引用对象（包括数组）时，“值”就是对对象的引用。
• 改变一个变量的值永远不会改变底层的原语或对象，它只是将变量指向一个新的原语或对象。
• 但是，更改变量引用的对象的属性确实会更改底层对象。

因此，要完成您的一些示例：

function f(a,b,c) {
    // Argument a is re-assigned to a new value.
    // The object or primitive referenced by the original a is unchanged.
    a = 3;
    // Calling b.push changes its properties - it adds
    // a new property b[b.length] with the value "foo".
    // So the object referenced by b has been changed.
    b.push("foo");
    // The "first" property of argument c has been changed.
    // So the object referenced by c has been changed (unless c is a primitive)
    c.first = false;
}

var x = 4;
var y = ["eeny", "miny", "mo"];
var z = {first: true};
f(x,y,z);
console.log(x, y, z.first); // 4, ["eeny", "miny", "mo", "foo"], false

示例 2：

var a = ["1", "2", {foo:"bar"}];
var b = a[1]; // b is now "2";
var c = a[2]; // c now references {foo:"bar"}
a[1] = "4";   // a is now ["1", "4", {foo:"bar"}]; b still has the value
              // it had at the time of assignment
a[2] = "5";   // a is now ["1", "4", "5"]; c still has the value
              // it had at the time of assignment, i.e. a reference to
              // the object {foo:"bar"}
console.log(b, c.foo); // "2" "bar"

Javascript总是按值传递。但是，如果将对象传递给函数，则“值”实际上是对该对象的引用，因此该函数可以修改该对象的属性，但不会导致函数外部的变量指向某个其他对象。

一个例子：

function changeParam(x, y, z) {
  x = 3;
  y = "new string";
  z["key2"] = "new";
  z["key3"] = "newer";

  z = {"new" : "object"};
}

var a = 1,
    b = "something",
    c = {"key1" : "whatever", "key2" : "original value"};

changeParam(a, b, c);

// at this point a is still 1
// b is still "something"
// c still points to the same object but its properties have been updated
// so it is now {"key1" : "whatever", "key2" : "new", "key3" : "newer"}
// c definitely doesn't point to the new object created as the last line
// of the function with z = ...

是的，Javascript 总是按值传递，但在数组或对象中，值是对它的引用，因此您可以“更改”内容。

但是，我认为您已经在 SO 上阅读了它；在这里你有你想要的文件：

http://snook.ca/archives/javascript/javascript_pass

1. 像字符串、数字这样的原始类型变量总是按值传递。

2. 数组和对象根据这两个条件作为按引用传递或按值传递。

   • 如果您正在使用新对象或数组更改该对象或数组的值，则它是按值传递的。

     object1 = {item: "car"}; array1=[1,2,3];

   在这里，您将新对象或数组分配给旧对象。您没有更改旧对象的属性值。因此它是按值传递的。

   • 如果您正在更改对象或数组的属性值，则它是通过引用传递的。

     object1.item= "car"; array1[0]=9;

   在这里，您正在更改旧对象的属性值。您没有将新对象或数组分配给旧对象。因此它是通过引用传递的。

代码

    function passVar(object1, object2, number1) {

        object1.key1= "laptop";
        object2 = {
            key2: "computer"
        };
        number1 = number1 + 1;
    }

    var object1 = {
        key1: "car"
    };
    var object2 = {
        key2: "bike"
    };
    var number1 = 10;

    passVar(object1, object2, number1);
    console.log(object1.key1);
    console.log(object2.key2);
    console.log(number1);

Output: -
    laptop
    bike
    10