Javascript中传递的是对象的引用。这意味着该对象从任何地方发生的更改都应该被反映出来。 在这种情况下，console.log(a)的期望输出结果是 {}。
function change(a,b) {
a.x = 'added';
a = b;//assigning a as {} to b
}
a={}
b={}
change(a,b);
console.log(a); //expected {} but output {x:'added'}
console.log(b)
这里发生了什么？据我所知，这不应该是由于函数作用域而引起的。 谢谢
如果您添加了另一行，您就可以更清楚地了解正在发生的事情：
function change(a,b) {
a.x = 'added';
a = b;
a.x = 'added as well';
};
a={};
b={};
change(a,b);
console.log(a); //{x:'added'}
console.log(b); //{x:'added as well'}
当您执行a = b时，您正在将本地变量a分配给b所持有的引用。
您说得没错，对象是按引用传递的，函数中对对象所做的任何更改都会在所有地方反映出来。这正是为什么在函数中添加x属性会修改它外部的对象。
您忽略了一点，即a = b;这行代码并未修改对象，而是修改了对象的引用。如果需要设置引用，可以将这两个对象放在另一个容器对象/数组中一起传入：
function change(container) {
container.a.x = 'added';
container.a = container.b;//assigning a as {} to b
}
var container = { a: {}, b: {}};
change(container);
console.log(container.a);
console.log(container.b)
a = b 只会修改本地引用（变量）！ - Bergifunction change(foo,bar) {
foo.x = 'added';
foo = bar;//assigning foo as {} to bar
}
a={}
b={}
change(a,b);
console.log(a); //expected {} but output {x:'added'}
console.log(b)
在这种情况下，很明显'foo'变量只存在于函数内部，而执行foo = bar不会改变a，因为引用是按值传递的。
function change(a,b) 创建了本地变量a和b，所以赋值a = b是针对本地变量a的赋值，而不是全局变量。 - RobGfoo 持有一个指向与 a 相同的对象的引用。foo 不是对 a 的引用。 - Bergifunction isEcmascriptPassByValue(foo) {
foo.push('More precisely, it is call-by-object-sharing!');
foo = 'No, ECMAScript is pass-by-reference.';
return;
}
var bar = ['Yes, of course, ECMAScript *is* pass-by-value!'];
isEcmascriptPassByValue(bar);
console.log(bar);
// Yes, of course, ECMAScript *is* pass-by-value!,
// More precisely, it is call-by-object-sharing!// In C#, struct defines a value type, class defines a reference type
struct MutableCell
{
public string value;
}
class Program
{
// the ref keyword means pass-by-reference, otherwise it's pass-by-value
// You must explicitly request pass-by-reference both at the definition and the call
static void IsCSharpPassByValue(string[] foo, MutableCell bar, ref string baz, ref MutableCell qux)
{
foo[0] = "More precisely, for reference types it is call-by-object-sharing, which is a special case of pass-by-value.";
foo = new string[] { "C# is not pass-by-reference." };
bar.value = "For value types, it is *not* call-by-sharing.";
bar = new MutableCell { value = "And also not pass-by-reference." };
baz = "It also supports pass-by-reference if explicitly requested.";
qux = new MutableCell { value = "Pass-by-reference is supported for value types as well." };
}
static void Main(string[] args)
{
var quux = new string[] { "Yes, of course, C# *is* pass-by-value!" };
var corge = new MutableCell { value = "For value types it is pure pass-by-value." };
var grault = "This string will vanish because of pass-by-reference.";
var garply = new MutableCell { value = "This string will vanish because of pass-by-reference." };
// the first two are passed by value, the other two by reference
IsCSharpPassByValue(quux, corge, ref grault, ref garply);
Console.WriteLine(quux[0]);
// More precisely, for reference types it is call-by-object-sharing, which is a special case of pass-by-value.
Console.WriteLine(corge.value);
// For value types it is pure pass-by-value.
Console.WriteLine(grault);
// It also supports pass-by-reference if explicitly requested.
Console.WriteLine(garply.value);
// Pass-by-reference is supported for value types as well.
}
}
好的，所以您已经发现JavaScript对象具有引用语义，因此修改引用会对原始作用域中的同一对象产生影响。
您还需要意识到的是，= 不属于这些规则的一部分；它不仅执行赋值操作，而且还将引用重新绑定到新对象。
从底层来看，这基本上就是您最初形成引用的方式。
function isEcmascriptPassByValue(foo) { foo = 'No, ECMAScript is pass-by-reference.'; return; }; var bar = 'Yes, of course, ECMAScript *is* pass-by-value!'; isEcmascriptPassByValue(bar); alert(bar); // Yes, of course, ECMAScript *is* pass-by-value! - Jörg W Mittag这应该能帮助您解决问题:
var obj = {}, anotherObj = {};
// in case if they are not global, make them global or define parent scope to be able to modify inside the function
window.obj = obj;
window.anotherObj = anotherObj;
function swap(a, b) {
window[a].newProp = 'XYZ';
window[a] = window[b]; // now obj is gone, because replaced with anotherObj
}
swap('obj','anotherObj');
console.log(obj); // now it would give Object {}
window对象，变量名作为字符串传递给函数。如果OP想要解决他的问题，而不仅仅是对发生了什么进行解释，这个解决方案正是他所需要的。 - iamawebgeek
b赋值给a没有任何效果，因为函数作用域中的a是一个不同的变量，而不是全局作用域中的a。 - GOTO 0foo和bar，那么可能更容易理解它的工作方式。 - Brandon