Javascript Objects Inside Array - Incorrectly Evaluating

Question

Why does the code below print "Tree", "Tree", and not "Bear", "Tree"?

var file_array = new Array(100);
var fileobject = {name: null , folder: null , url: null , modified: null};

fileobject.name = "Bear";
file_array[0] = fileobject;
fileobject.name = "Tree";
file_array[1] = fileobject;

console.log(file_array[0].name);
console.log(file_array[1].name);

Pointy · Accepted Answer · 2017-02-16 16:09:14Z

2

There's only one object involved. Assigning an object value with = assigns a reference to the object, not a copy.

It's possible to copy objects, but in the general case it can grow to a very hard problem (due to things like reference cycles). If you need lots of those objects, a better solution would be to write a function that returns a fresh object when you call it:

function makeFileObject(name) {
  return {name: name , folder: null , url: null , modified: null};
}

file_array[0] = makeFileObject("Bear");
file_array[1] = makeFileObject("Tree");

answered Feb 16, 2017 at 16:09

Pointy

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1 Comment

Steve Over a year ago

Thanks a lot, been pulling my hair out over this one!

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