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

Question

Pretty self evident question...When using .push() on an array in javascript, is the object pushed into the array a pointer (shallow) or the actual object (deep) regardless of type.

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