I’m confused about how JavaScript deals with passing arguments to functions. I know that numbers and strings are passed by value, but what about objects? Sometimes it seems like they’re passed by value, and other times by reference.
Here’s what I mean:
function modifyValues(x, y, z) {
x = x * 10;
y.detail = "modified";
z = {detail: "modified"};
}
let value = 10;
let objectOne = {detail: "unchanged"};
let objectTwo = {detail: "unchanged"};
modifyValues(value, objectOne, objectTwo);
console.log(value); // Still 10
console.log(objectOne.detail); // Now "modified"
console.log(objectTwo.detail); // Still "unchanged"
This behavior is puzzling. Could someone explain what’s actually happening and whether the JavaScript specification provides an official explanation for this?
JavaScript’s parameter passing can indeed be confusing at first glance. The key is understanding that JavaScript always passes by value, but for objects, the value passed is a reference to the object.
When you pass a primitive (like a number), you’re passing a copy of that value. Modifying it inside the function doesn’t affect the original.
For objects, you’re passing a copy of the reference. This means you can modify the object’s properties (as seen with objectOne), and those changes will be reflected outside the function. However, reassigning the parameter to a new object (such as objectTwo) simply changes the local reference, not the original object.
This behavior aligns with the ECMAScript specifications and is often described as ‘pass by sharing.’ Understanding this concept is crucial for effective JavaScript programming and helps avoid unintended side effects.
As someone who’s been knee-deep in JavaScript for years, I can relate to your confusion. The behavior you’re seeing is a result of JavaScript’s unique approach to parameter passing.
In my experience, it’s helpful to think of it this way: JavaScript always passes by value, but for objects, that value is actually a reference. It’s like giving someone directions to your house versus giving them a copy of your house.
When you pass a primitive like a number, it’s like giving a copy. They can’t change your original number. But with objects, you’re giving directions. They can follow those directions and change what’s inside, but if they throw away the directions and get new ones, it doesn’t affect your original object.
This concept took me a while to grasp fully, but once it clicks, it makes JavaScript’s behavior much more predictable. It’s not a bug, it’s a feature - albeit a tricky one!
javascript’s weird like that, man. it’s all about references n stuff. objects kinda act different from numbers. when u pass an object, ur basically giving the function a ‘pointer’ to it. so if u mess with the inside, it changes the original. but if u try to replace the whole thing, it don’t work outside the function. confusing, but thats how it rolls