我的理解是，这实际上非常简单：
因此，通过一些示例：
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
范例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"
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