Do objects pushed into an array in javascript deep or shallow copy?

Question

很明显的问题...当在javascript中的数组上使用.push（）时，对象是指针（浅）还是实际对象（深）推入数组， 而不管类型如何 。

Answer 1

It depends upon what you're pushing. Objects and arrays are pushed as a pointer to the original object . Built-in primitive types like numbers or booleans are pushed as a copy. So, since objects are not copied in any way, there's no deep or shallow copy for them.

Here's a working snippet that shows it:

var array = [];
var x = 4;
let y = {name: "test", type: "data", data: "2-27-2009"};

// primitive value pushes a copy of the value 4
array.push(x);                // push value of 4
x = 5;                        // change x to 5
console.log(array[0]);        // array still contains 4 because it's a copy

// object reference pushes a reference
array.push(y);                // put object y reference into the array
y.name = "foo";               // change y.name property
console.log(array[1].name);   // logs changed value "foo" because it's a reference    

// object reference pushes a reference but object can still be referred to even though original variable is no longer within scope
if (true) {
    let z = {name: "test", type: "data", data: "2-28-2019"};
    array.push(z);
}

console.log(array[2].name);   // log shows value "test" since the pointer reference via the array is still within scope

Answer 2

jfriend00 is right on the mark here, but one small clarification: That doesn't mean you can't change what your variable is pointing to. That is, y initially references some variable that you put into the array, but you can then take the variable named y , disconnect it from the object that's in the array now, and connect y (ie, make it reference ) something different entirely without changing the object that now is referenced only by the array .

http://jsfiddle.net/rufwork/5cNQr/6/

var array = [];
var x = 4;
var y = {name: "test", type: "data", data: "2-27-2009"};

// 1.) pushes a copy
array.push(x);
x = 5;
document.write(array[0] + "<br>");    // alerts 4 because it's a copy

// 2.) pushes a reference
array.push(y);
y.name = "foo";

// 3.) Disconnects y and points it at a new object
y = {}; 
y.name = 'bar';
document.write(array[1].name + ' :: ' + y.name + "<br>");   
// alerts "foo :: bar" because y was a reference, but then 
// the reference was moved to a new object while the 
// reference in the array stayed the same (referencing the 
// original object)

// 4.) Uses y's original reference, stored in the array,
// to access the old object.
array[1].name = 'foobar';
document.write(array[1].name + "<br>");
// alerts "foobar" because you used the array to point to 
// the object that was initially in y.

Answer 3

We can clear the pointer by passing the object/array via json stringify and then parse

newobj.push(JSON.parse(JSON.stringify(obj)));

I hope it helps someone, hence I posted.