How to get the size of a JavaScript object?

Look to the bottom od these posts to get my latest answer. I have re-factored the code in my original answer. I have removed the recursion and removed the assumed existence overhead. This is a new edit to bring it little more up-to-date in style.

function roughSizeOfObject(object) { const objectList = []; const stack = [object]; let bytes = 0; while (stack.length) { const value = stack.pop(); switch (typeof value) { case 'boolean': bytes += 4; break; case 'string': bytes += value.length * 2; break; case 'number': bytes += 8; break; case 'object': if (!objectList.includes(value)) { objectList.push(value); for (const prop in value) { if (value.hasOwnProperty(prop)) { stack.push(value[prop]); } } } break; } } return bytes; } 

The Google Chrome Heap Profiler allows you to inspect object memory use.

You need to be able to locate the object in the trace which can be tricky. If you pin the object to the Window global, it is pretty easy to find from the "Containment" listing mode.

In the attached screenshot, I created an object called "testObj" on the window. I then located in the profiler (after making a recording) and it shows the full size of the object and everything in it under "retained size".

More details on the memory breakdowns.

In the above screenshot, the object shows a retained size of 60. I believe the unit is bytes here.

Sometimes I use this to flag really big objects that might be going to the client from the server. It doesn't represent the in memory footprint. It just gets you approximately what it'd cost to send it, or store it.

Also note, it's slow, dev only. But for getting an ballpark answer with one line of code it's been useful for me.

roughObjSize = JSON.stringify(bigObject).length; 

I just wrote this to solve a similar (ish) problem. It doesn't exactly do what you may be looking for, ie it doesn't take into account how the interpreter stores the object.

But, if you are using V8, it should give you a fairly ok approximation as the awesome prototyping and hidden classes lick up most of the overhead.

function roughSizeOfObject( object ) { var objectList = []; var recurse = function( value ) { var bytes = 0; if ( typeof value === 'boolean' ) { bytes = 4; } else if ( typeof value === 'string' ) { bytes = value.length * 2; } else if ( typeof value === 'number' ) { bytes = 8; } else if ( typeof value === 'object' && objectList.indexOf( value ) === -1 ) { objectList[ objectList.length ] = value; for( i in value ) { bytes+= 8; // an assumed existence overhead bytes+= recurse( value[i] ) } } return bytes; } return recurse( object ); } 

Here's a slightly more compact solution to the problem:

const typeSizes = { "undefined": () => 0, "boolean": () => 4, "number": () => 8, "string": item => 2 * item.length, "object": item => !item ? 0 : Object .keys(item) .reduce((total, key) => sizeOf(key) + sizeOf(item[key]) + total, 0) }; const sizeOf = value => typeSizes[typeof value](value); 

There is a NPM module to get object sizeof, you can install it with npm install object-sizeof

 var sizeof = require('object-sizeof'); // 2B per character, 6 chars total => 12B console.log(sizeof({abc: 'def'})); // 8B for Number => 8B console.log(sizeof(12345)); var param = { 'a': 1, 'b': 2, 'c': { 'd': 4 } }; // 4 one two-bytes char strings and 3 eighth-bytes numbers => 32B console.log(sizeof(param)); 

This is a hacky method, but i tried it twice with different numbers and it seems to be consistent.

What you can do is to try and allocate a huge number of objects, like one or two million objects of the kind you want. Put the objects in an array to prevent the garbage collector from releasing them (note that this will add a slight memory overhead because of the array, but i hope this shouldn't matter and besides if you are going to worry about objects being in memory, you store them somewhere). Add an alert before and after the allocation and in each alert check how much memory the Firefox process is taking. Before you open the page with the test, make sure you have a fresh Firefox instance. Open the page, note the memory usage after the "before" alert is shown. Close the alert, wait for the memory to be allocated. Subtract the new memory from the older and divide it by the amount of allocations. Example:

function Marks() { this.maxMarks = 100; } function Student() { this.firstName = "firstName"; this.lastName = "lastName"; this.marks = new Marks(); } var manyObjects = new Array(); alert('before'); for (var i=0; i<2000000; i++) manyObjects[i] = new Student(); alert('after'); 

I tried this in my computer and the process had 48352K of memory when the "before" alert was shown. After the allocation, Firefox had 440236K of memory. For 2million allocations, this is about 200 bytes for each object.

I tried it again with 1million allocations and the result was similar: 196 bytes per object (i suppose the extra data in 2mill was used for Array).

So, here is a hacky method that might help you. JavaScript doesn't provide a "sizeof" method for a reason: each JavaScript implementaion is different. In Google Chrome for example the same page uses about 66 bytes for each object (judging from the task manager at least).

Sorry I could not comment, so I just continue the work from tomwrong. This enhanced version will not count object more than once, thus no infinite loop. Plus, I reckon the key of an object should be also counted, roughly.

function roughSizeOfObject( value, level ) { if(level == undefined) level = 0; var bytes = 0; if ( typeof value === 'boolean' ) { bytes = 4; } else if ( typeof value === 'string' ) { bytes = value.length * 2; } else if ( typeof value === 'number' ) { bytes = 8; } else if ( typeof value === 'object' ) { if(value['__visited__']) return 0; value['__visited__'] = 1; for( i in value ) { bytes += i.length * 2; bytes+= 8; // an assumed existence overhead bytes+= roughSizeOfObject( value[i], 1 ) } } if(level == 0){ clear__visited__(value); } return bytes; } function clear__visited__(value){ if(typeof value == 'object'){ delete value['__visited__']; for(var i in value){ clear__visited__(value[i]); } } } roughSizeOfObject(a); 

Having the same problem. I searched on Google and I want to share with stackoverflow community this solution.

Important:

I used the function shared by Yan Qing on github https://gist.github.com/zensh/4975495

function memorySizeOf(obj) { var bytes = 0; function sizeOf(obj) { if(obj !== null && obj !== undefined) { switch(typeof obj) { case 'number': bytes += 8; break; case 'string': bytes += obj.length * 2; break; case 'boolean': bytes += 4; break; case 'object': var objClass = Object.prototype.toString.call(obj).slice(8, -1); if(objClass === 'Object' || objClass === 'Array') { for(var key in obj) { if(!obj.hasOwnProperty(key)) continue; sizeOf(obj[key]); } } else bytes += obj.toString().length * 2; break; } } return bytes; }; function formatByteSize(bytes) { if(bytes < 1024) return bytes + " bytes"; else if(bytes < 1048576) return(bytes / 1024).toFixed(3) + " KiB"; else if(bytes < 1073741824) return(bytes / 1048576).toFixed(3) + " MiB"; else return(bytes / 1073741824).toFixed(3) + " GiB"; }; return formatByteSize(sizeOf(obj)); }; var sizeOfStudentObject = memorySizeOf({Student: {firstName: 'firstName', lastName: 'lastName', marks: 10}}); console.log(sizeOfStudentObject);

What do you think about it?

i want to know if my memory reduction efforts actually help in reducing memory

Following up on this comment, here's what you should do: Try to produce a memory problem - Write code that creates all these objects and graudally increase the upper limit until you ran into a problem (Browser crash, Browser freeze or an Out-Of-memory error). Ideally you should repeat this experiment with different browsers and different operating system.

Now there are two options: option 1 - You didn't succeed in producing the memory problem. Hence, you are worrying for nothing. You don't have a memory issue and your program is fine.

option 2- you did get a memory problem. Now ask yourself whether the limit at which the problem occurred is reasonable (in other words: is it likely that this amount of objects will be created at normal use of your code). If the answer is 'No' then you're fine. Otherwise you now know how many objects your code can create. Rework the algorithm such that it does not breach this limit.

This Javascript library sizeof.js does the same thing. Include it like this

<script type="text/javascript" src="sizeof.js"></script> 

The sizeof function takes an object as a parameter and returns its approximate size in bytes. For example:

// define an object var object = { 'boolean' : true, 'number' : 1, 'string' : 'a', 'array' : [1, 2, 3] }; // determine the size of the object var size = sizeof(object); 

The sizeof function can handle objects that contain multiple references to other objects and recursive references.

Originally published here.

If your main concern is the memory usage of your Firefox extension, I suggest checking with Mozilla developers.

Mozilla provides on its wiki a list of tools to analyze memory leaks.

Chrome developer tools has this functionality. I found this article very helpful and does exactly what you want: https://developers.google.com/chrome-developer-tools/docs/heap-profiling

The accepted answer does not work with Map, Set, WeakMap and other iterable objects. (The package object-sizeof, mentioned in other answer, has the same problem).

Here's my fix

export function roughSizeOfObject(object) { const objectList = []; const stack = [object]; const bytes = [0]; while (stack.length) { const value = stack.pop(); if (value == null) bytes[0] += 4; else if (typeof value === 'boolean') bytes[0] += 4; else if (typeof value === 'string') bytes[0] += value.length * 2; else if (typeof value === 'number') bytes[0] += 8; else if (typeof value === 'object' && objectList.indexOf(value) === -1) { objectList.push(value); if (typeof value.byteLength === 'number') bytes[0] += value.byteLength; else if (value[Symbol.iterator]) { // eslint-disable-next-line no-restricted-syntax for (const v of value) stack.push(v); } else { Object.keys(value).forEach(k => { bytes[0] += k.length * 2; stack.push(value[k]); }); } } } return bytes[0]; } 

It also includes some other minor improvements: counts keys storage and works with ArrayBuffer.

function sizeOf(parent_data, size) { for (var prop in parent_data) { let value = parent_data[prop]; if (typeof value === 'boolean') { size += 4; } else if (typeof value === 'string') { size += value.length * 2; } else if (typeof value === 'number') { size += 8; } else { let oldSize = size; size += sizeOf(value, oldSize) - oldSize; } } return size; } function roughSizeOfObject(object) { let size = 0; for each (let prop in object) { size += sizeOf(prop, 0); } // for.. return size; } 

Many thanks to everyone that has been working on code for this!

I just wanted to add that I've been looking for exactly the same thing, but in my case it's for managing a cache of processed objects to avoid having to re-parse and process objects from ajax calls that may or may not have been cached by the browser. This is especially useful for objects that require a lot of processing, usually anything that isn't in JSON format, but it can get very costly to keep these things cached in a large project or an app/extension that is left running for a long time.

Anyway, I use it for something something like:

var myCache = { cache: {}, order: [], size: 0, maxSize: 2 * 1024 * 1024, // 2mb add: function(key, object) { // Otherwise add new object var size = this.getObjectSize(object); if (size > this.maxSize) return; // Can't store this object var total = this.size + size; // Check for existing entry, as replacing it will free up space if (typeof(this.cache[key]) !== 'undefined') { for (var i = 0; i < this.order.length; ++i) { var entry = this.order[i]; if (entry.key === key) { total -= entry.size; this.order.splice(i, 1); break; } } } while (total > this.maxSize) { var entry = this.order.shift(); delete this.cache[entry.key]; total -= entry.size; } this.cache[key] = object; this.order.push({ size: size, key: key }); this.size = total; }, get: function(key) { var value = this.cache[key]; if (typeof(value) !== 'undefined') { // Return this key for longer for (var i = 0; i < this.order.length; ++i) { var entry = this.order[i]; if (entry.key === key) { this.order.splice(i, 1); this.order.push(entry); break; } } } return value; }, getObjectSize: function(object) { // Code from above estimating functions }, }; 

It's a simplistic example and may have some errors, but it gives the idea, as you can use it to hold onto static objects (contents won't change) with some degree of intelligence. This can significantly cut down on any expensive processing requirements that the object had to be produced in the first place.

I use Chrome dev tools' Timeline tab, instantiate increasingly large amounts of objects, and get good estimates like that. You can use html like this one below, as boilerplate, and modify it to better simulate the characteristics of your objects (number and types of properties, etc...). You may want to click the trash bit icon at the bottom of that dev tools tab, before and after a run.

<html> <script> var size = 1000*100 window.onload = function() { document.getElementById("quantifier").value = size } function scaffold() { console.log("processing Scaffold..."); a = new Array } function start() { size = document.getElementById("quantifier").value console.log("Starting... quantifier is " + size); console.log("starting test") for (i=0; i<size; i++){ a[i]={"some" : "thing"} } console.log("done...") } function tearDown() { console.log("processing teardown"); a.length=0 } </script> <body> <span style="color:green;">Quantifier:</span> <input id="quantifier" style="color:green;" type="text"></input> <button onclick="scaffold()">Scaffold</button> <button onclick="start()">Start</button> <button onclick="tearDown()">Clean</button> <br/> </body> </html> 

Instantiating 2 million objects of just one property each (as in this code above) leads to a rough calculation of 50 bytes per object, on my Chromium, right now. Changing the code to create a random string per object adds some 30 bytes per object, etc. Hope this helps.

I had problems with the above answer with an ArrayBuffer. After checking the documentation, I found that ArrayBuffer has a byteLength property which tells me exactly what I need, hence:

function sizeOf(data) { if (typeof(data) === 'object') { if (data instanceof ArrayBuffer) { return data.byteLength; } // other objects goes here } // non-object cases goes here } console.log(sizeOf(new ArrayBuffer(15))); // 15

Reference:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/byteLength

Building upon the already compact solution from @Dan, here's a self-contained function version of it. Variable names are reduced to single letters for those who just want it to be as compact as possible at the expense of context.

const ns = {}; ns.sizeof = function(v) { let f = ns.sizeof, //this needs to match the name of the function itself, since arguments.callee.name is defunct o = { "undefined": () => 0, "boolean": () => 4, "number": () => 8, "string": i => 2 * i.length, "object": i => !i ? 0 : Object .keys(i) .reduce((t, k) => f(k) + f(i[k]) + t, 0) }; return o[typeof v](v); }; ns.undef; ns.bool = true; ns.num = 1; ns.string = "Hello"; ns.obj = { first_name: 'John', last_name: 'Doe', born: new Date(1980, 1, 1), favorite_foods: ['Pizza', 'Salad', 'Indian', 'Sushi'], can_juggle: true }; console.log(ns.sizeof(ns.undef)); console.log(ns.sizeof(ns.bool)); console.log(ns.sizeof(ns.num)); console.log(ns.sizeof(ns.string)); console.log(ns.sizeof(ns.obj)); console.log(ns.sizeof(ns.obj.favorite_foods));

This is another improvement to my original answer as things have moved forward.

function roughSizeOfObject(object) { const stack = [object]; const seen = new WeakSet(); let bytes = 0; while (stack.length) { const value = stack.pop(); switch (typeof value) { case 'boolean': bytes += 4; break; case 'string': bytes += value.length * 2; // UTF-16 assumption break; case 'number': bytes += 8; // IEEE-754 double break; case 'bigint': bytes += 8; // very rough break; case 'symbol': case 'function': case 'undefined': break; case 'object': if (value === null) break; if (seen.has(value)) break; seen.add(value); // Count object overhead – completely engine-dependent bytes += 16; // Handle Maps, Sets, etc. if (value instanceof Map) { stack.push(...value.keys(), ...value.values()); break; } if (value instanceof Set) { stack.push(...value.values()); break; } if (ArrayBuffer.isView(value)) { bytes += value.byteLength; break; } if (value instanceof ArrayBuffer) { bytes += value.byteLength; break; } // Walk own keys (including non-enumerable & symbols) for (const key of Reflect.ownKeys(value)) { bytes += key.toString().length * 2; // key size stack.push(value[key]); } break; } } return bytes; }