04_pass-by-value-reference.md

pass-by value and pass-by reference

• The primitive type such as strings, numbers, booleans are pass-by value and objects is pass-by reference.
• pass-by value is to pass a copy.
• pass-by reference is to pass a pointer.

Example 1

• pass-by value
• The variable a in foo function is only visible inside the foo function.

"use strict";

var a = 1;
function foo(a){
  a = 2;
}
foo(a);
console.log(a); //1

Example 2

• objects is pass-by reference.

"use strict";

var a = {};
function foo(a){
  a.firstname = "Hiroko";
}
foo(a);
console.log(a); //{firstname: "Hiroko"}

Example 3

• when you change the object, we have to change a property NOT an object itself.

"use strict";

var a = {"moo": "foo"};
function foo(a){
  //a = {"moo": "goo"}; // we can't change a object. we can only change the property.
  a.moo = 'goo';
}
foo(a);
console.log(a); //{moo: "goo"}