JavaScript是按引用传递还是按值传递语言？ 原始类型（数字、字符串等）是通过值传递的，但对象是未知的，因为它们都可以通过值传递（如果我们认为持有对象的变量实际上是对对象的引用），并通过引用传递（当我们考虑到对象的变量持有对象本身）时，

虽然这在最后并不重要，但我想知道用什么正确的方式来表示通过约定的参数。是否有来自JavaScript规范的摘录，其中定义了与此相关的语义？

有一些关于在JavaScript中使用术语“通过引用传递”的讨论，但为了回答您的问题：

对象是通过引用自动传递的，无需特别声明它

（来自上面提到的文章。）

变量不“持有”对象；它有一个参考。您可以将该引用指定给另一个变量，现在两者都引用同一个对象。它总是通过值传递（即使该值是引用…）

无法更改作为参数传递的变量所持有的值，如果JavaScript支持按引用传递，这是可能的。

JavaScript总是按值传递；一切都是价值型的

对象是值，对象的成员函数本身就是值（记住，函数在JavaScript中是一级对象）。另外，关于JavaScript中的一切都是对象的概念；这是错误的。字符串、符号、数字、布尔值、空值和未定义项都是基元

有时，它们可以利用从基本原型继承的一些成员函数和属性，但这只是为了方便。这并不意味着它们本身就是对象。请尝试以下内容以供参考：

x = "test";
alert(x.foo);
x.foo = 12;
alert(x.foo);

---

在这两个警报中，您会发现值未定义。

确定某个内容是否为“按引用传递”的简单方法是您是否可以编写“交换”函数。例如，在C中，您可以执行以下操作：

void swap(int *i, int *j)
{
    int t;
    t = *i;
    *i = *j;
    *j = t;
}

---

如果你不能在JavaScript中做到这一点，那就不是“通过引用传递”。

这在JavaScript中很有趣。考虑这个例子：

函数变换器（a、b、c）
{
a=a*10；
b、 item=“已更改”；
c={项目：“已更改”}；
}
var-num=10；
var obj1={item:“unchanged”}；
var obj2={item:“unchanged”}；
变更对象（num、obj1、obj2）；
console.log（num）；
控制台日志（obj1.item）；
console.log（obj2.item）它总是按值传递，但对于对象，变量的值是一个引用。因此，当您传递一个对象并更改其成员时，这些更改将保留在函数之外。这使它看起来像是通过引用传递的。但是，如果您实际更改了对象变量的值，您将看到更改不会持续，从而证明它确实是通过值传递的

例如：


函数changeObject（x）{
x={成员：“条”}；
console.log（“in changeObject:+x.member”）；
}
功能更改成员（x）{
x、 member=“bar”；
console.log（“in changember:+x.member”）；
}
var x={成员：“foo”}；
console.log（“更改对象之前：+x.member”）；
变更对象（x）；
console.log（“在changeObject之后：+x.member）；/*变化并未持续*/
console.log（“变更前成员：+x.member”）；
变更成员（x）；
console.log（“变更后成员：+x.member”）；/*更改依然存在*/
关于复制、传递和比较的详细说明，请参见“JavaScript:最终指南”一书

在我们离开这个话题之前
通过
参考资料，我们需要澄清一点
命名法

“路过”一词
“reference”可以有多种含义。
对一些读者来说，这个短语指的是
一种函数调用技术
允许函数指定新值
它的论点，并有这些
修改后的值在外部可见
功能。这不是这个术语的用法
这本书中使用了

这里，我们的意思是
简单地说就是对一个对象的引用
或数组，而不是对象本身--
传递给函数。函数
可以使用引用进行修改
对象或元素的属性
数组的一部分。但是如果函数
用一个
对新对象或数组的引用，
这种修改是不可见的
在功能之外

var myObject = {
    firstName: 'Joe',
    lastName: 'Smith'
};

// Assign to a new variable (just like when you pass to a function)
var otherObj = myObject;

// Let's mutate our object
otherObj.firstName = 'Sue'; // I guess Joe decided to be a girl

console.log(myObject.firstName); // Logs 'Sue'
console.log(otherObj.firstName); // Logs 'Sue'

// Now, let's reassign the variable
otherObj = {
    firstName: 'Jack',
    lastName: 'Frost'
};

// Now, otherObj and myObject are assigned to 2 very different objects
// And mutating one object has no influence on the other
console.log(myObject.firstName); // Logs 'Sue'
console.log(otherObj.firstName); // Logs 'Jack';

读者
熟悉
这个术语可能更倾向于这样说
对象和数组通过
值，但传递的值为
实际上是一个参考，而不是
对象本身

函数外部的对象通过引用外部对象传递到函数中

当您使用该引用操纵其对象时，外部对象将因此受到影响。但是，如果在函数内部决定将引用指向其他对象，则根本不会影响外部对象，因为您所做的只是将引用重新指向其他对象
 我发现，当我想将对象作为参数传入时，这个函数非常有用，它可以被修改或完全替换

function replaceOrModify(aObj) {
  if (modify) {

    aObj.setNewValue('foo');

  } else {

   var newObj = new MyObject();
   // _.extend(destination, *sources) 
   _.extend(newObj, aObj);
  }
}

原语（数字、布尔值等）按值传递。

字符串是不可变的，所以这对它们来说并不重要

对象通过引用传递（引用通过值传递）
我发现最简洁的解释是：


基本体：当您访问基本体类型时，您直接在其上工作
价值观


串
数
布尔值
空的
未定义


例如：


Complex：访问复杂类型时，处理对其值的引用


反对
排列
作用


例如：

也就是说，基本类型实际上是通过值传递的，复杂类型是通过引用传递的。
我的两分钱。。。这
var foo = [1, 2],
    bar = foo;

bar[0] = 9;

console.log(foo[0], bar[0]); // => 9, 9

var object1 = {};
var object2 = {};

var favoriteObject = object1;

favoriteObject = object2;

object2.name = 'Fred';
console.log(favoriteObject.name) // Logs Fred
favoriteObject.name = 'Joe';
console.log(object2.name); // Logs Joe

var string1 = 'Hello world';
var string2 = 'Goodbye world';

var favoriteString = string1;

favoriteString = 'Hello everyone';
console.log(favoriteString); // Logs 'Hello everyone'
console.log(string1); // Logs 'Hello world'

var myString = 'hello';

// Assign to a new variable (just like when you pass to a function)
var param1 = myString;
param1 = 'world'; // Re assignment

console.log(myString); // Logs 'hello'
console.log(param1);   // Logs 'world'

function myFunc(param1) {
    param1 = 'world';

    console.log(param1);   // Logs 'world'
}

var myString = 'hello';
// Calls myFunc and assigns param1 to myString just like param1 = myString
myFunc(myString);

console.log(myString); // logs 'hello'

var myObject = {
    firstName: 'Joe',
    lastName: 'Smith'
};

// Assign to a new variable (just like when you pass to a function)
var otherObj = myObject;

// Let's mutate our object
otherObj.firstName = 'Sue'; // I guess Joe decided to be a girl

console.log(myObject.firstName); // Logs 'Sue'
console.log(otherObj.firstName); // Logs 'Sue'

// Now, let's reassign the variable
otherObj = {
    firstName: 'Jack',
    lastName: 'Frost'
};

// Now, otherObj and myObject are assigned to 2 very different objects
// And mutating one object has no influence on the other
console.log(myObject.firstName); // Logs 'Sue'
console.log(otherObj.firstName); // Logs 'Jack';

function myFunc(otherObj) {

    // Let's mutate our object
    otherObj.firstName = 'Sue';
    console.log(otherObj.firstName); // Logs 'Sue'

    // Now let's re-assign
    otherObj = {
        firstName: 'Jack',
        lastName: 'Frost'
    };
    console.log(otherObj.firstName); // Logs 'Jack'

    // Again, otherObj and myObject are assigned to 2 very different objects
    // And mutating one object doesn't magically mutate the other
}

var myObject = {
    firstName: 'Joe',
    lastName: 'Smith'
};

// Calls myFunc and assigns otherObj to myObject just like otherObj = myObject
myFunc(myObject);

console.log(myObject.firstName); // Logs 'Sue', just like before

function myFunc(myString) {
    // myString is private and does not affect the outer variable
    myString = 'hello';
}

var myString = 'test';
myString = myString; // Does nothing, myString is still 'test';

myFunc(myString);
console.log(myString); // Logs 'test'

var var1 = 13;
var var2 = { prop: 2 };

//13 and var2's content (reference) are being passed here
foo(var1, var2); 

function foo(inVar1, inVar2){
    //changing contents of inVar1 and inVar2 won't affect variables outside
    inVar1 = 20;
    inVar2 = { prop: 7 };
}

function foo(inVar1, inVar2){
    inVar2.prop = 7; 
}

    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

/*
The following C program demonstrates how arguments
to JavaScript functions are passed in a way analogous
to pass-by-pointer-value in C. The original JavaScript
test case by @Shog9 follows with the translation of
the code into C. This should make things clear to
those transitioning from C to JavaScript.

function changeStuff(num, obj1, obj2)
{
    num = num * 10;
    obj1.item = "changed";
    obj2 = {item: "changed"};
}

var num = 10;
var obj1 = {item: "unchanged"};
var obj2 = {item: "unchanged"};
changeStuff(num, obj1, obj2);
console.log(num);
console.log(obj1.item);    
console.log(obj2.item);

This produces the output:

10
changed
unchanged
*/

#include <stdio.h>
#include <stdlib.h>

struct obj {
    char *item;
};

void changeStuff(int *num, struct obj *obj1, struct obj *obj2)
{
    // make pointer point to a new memory location
    // holding the new integer value
    int *old_num = num;
    num = malloc(sizeof(int));
    *num = *old_num * 10;
    // make property of structure pointed to by pointer
    // point to the new value
    obj1->item = "changed";
    // make pointer point to a new memory location
    // holding the new structure value
    obj2 = malloc(sizeof(struct obj));
    obj2->item = "changed";
    free(num); // end of scope
    free(obj2); // end of scope
}

int num = 10;
struct obj obj1 = { "unchanged" };
struct obj obj2 = { "unchanged" };

int main()
{
    // pass pointers by value: the pointers
    // will be copied into the argument list
    // of the called function and the copied
    // pointers will point to the same values
    // as the original pointers
    changeStuff(&num, &obj1, &obj2);
    printf("%d\n", num);
    puts(obj1.item);
    puts(obj2.item);
    return 0;
}

function changePrimitive(val) {
    // At this point there are two '10's in memory.
    // Changing one won't affect the other
    val = val * 10;
}
var x = 10;
changePrimitive(x);
// x === 10

function changeObject(obj) {
    // At this point there are two references (x and obj) in memory,
    // but these both point to the same object.
    // changing the object will change the underlying object that
    // x and obj both hold a reference to.
    obj.val = obj.val * 10;
}
var x = { val: 10 };
changeObject(x);
// x === { val: 100 }

function changeObject(obj) {
    // Again there are two references (x and obj) in memory,
    // these both point to the same object.
    // now we create a completely new object and assign it.
    // obj's reference now points to the new object.
    // x's reference doesn't change.
    obj = { val: 100 };
}
var x = { val: 10 };
changeObject(x);
// x === { val: 10}

// code
var obj = {
    name: 'Fred',
    num: 1
};

// illustration
               'Fred'
              /
             /
(obj) ---- {}
             \
              \
               1

// code
obj.name = 'George';


// illustration
                 'Fred'


(obj) ---- {} ----- 'George'
             \
              \
               1

// code
obj = {};

// illustration
                 'Fred'


(obj)      {} ----- 'George'
  |          \
  |           \
 { }            1

// code
var obj = {
    text: 'Hello world!'
};

/* function parameters get their own pointer to 
 * the arguments that are passed in, just like any other variable */
someFunc(obj);


// illustration
(caller scope)        (someFunc scope)
           \             /
            \           /
             \         /
              \       /
               \     /
                 { }
                  |
                  |
                  |
            'Hello world'

var a = [1,2];
var b = a;

a = [];
console.log(b); // [1,2]
// doesn't work because `b` is still pointing at the original array

var a = 2;
var b = a; // `b` is always a copy of the value in `a`
b++;
a; // 2
b; // 3

var c = [1,2,3];
var d = c; // `d` is a reference to the shared `[1,2,3]` value
d.push( 4 );
c; // [1,2,3,4]
d; // [1,2,3,4]

var a = [1,2,3];
var b = a;
a; // [1,2,3]
b; // [1,2,3]

// later
b = [4,5,6];
a; // [1,2,3]
b; // [4,5,6]

function foo(x) {
    x.push( 4 );
    x; // [1,2,3,4]

    // later
    x = [4,5,6];
    x.push( 7 );
    x; // [4,5,6,7]
}

var a = [1,2,3];

foo( a );

a; // [1,2,3,4]  not  [4,5,6,7]

foo( a.slice() );

function foo(wrapper) {
    wrapper.a = 42;
}

var obj = {
    a: 2
};

foo( obj );

obj.a; // 42

int myAge = 14;
increaseAgeByRef(myAge);
function increaseAgeByRef(int &age) {
  *age = *age + 1;
}

var a = 3;
var b = a;

console.log(a); // a = 3
console.log(b); // b = 3

a=4;
console.log(a); // a = 4
console.log(b); // b = 3

var c = { "name" : "john" };
var d = c;

console.log(c); // { "name" : "john" }
console.log(d); // { "name" : "john" }

c.name = "doe";

console.log(c); // { "name" : "doe" }
console.log(d); // { "name" : "doe" }

c = {"name" : "jane"};
console.log(c); // { "name" : "jane" }
console.log(d); // { "name" : "doe" }

let arr = [1, 2, 3, 4, 5]; //arr is an object now and a purple arrow is indicating it
let obj2 = arr; // now, obj2 is another purple arrow that is indicating the value of arr obj
let obj3 = ['a', 'b', 'c'];
obj2.push(6); // first pic below - making a new hand for the blue circle to point the 6
//obj2 = [1, 2, 3, 4, 5, 6]
//arr = [1, 2, 3, 4, 5, 6]
//we changed the blue circle object value (type1-value) and due to arr and obj2 are indicating that so both of them changed
obj2 = obj3; //next pic below - changing the direction of obj2 array from blue circle to orange circle so obj2 is no more [1,2,3,4,5,6] and it's no more about changing anything in it but we completely changed its direction and now obj2 is pointing to obj3
//obj2 = ['a', 'b', 'c'];
//obj3 = ['a', 'b', 'c'];

// Copy JS object without reference
var first = {"a":"value1","b":"value2"};
var clone = JSON.parse( JSON.stringify( first ) ); 

var second = ["a","b","c"];
var clone = JSON.parse( JSON.stringify( second ) ); 

 let a = { prop: 1 };
 let b = a; // a and b hold the same value
 a.prop = "test"; // The object gets mutated, can be observed through both a and b
 b = { prop: 2 }; // b holds now a different value