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calculate memory size of javascript object, it is not a accurate value!
function memorySizeOf(obj) {
var bytes = 0;
function sizeOf(obj) {
if(obj !== null && obj !== undefined) {
switch(typeof obj) {
case 'number':
bytes += 8;
case 'string':
bytes += obj.length * 2;
case 'boolean':
bytes += 4;
case 'object':
var objClass =, -1);
if(objClass === 'Object' || objClass === 'Array') {
for(var key in obj) {
if(!obj.hasOwnProperty(key)) continue;
} else bytes += obj.toString().length * 2;
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));
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why boolean is 4 bytes? Maybe you have spec link?


A boolean is actually 1 byte. But alignment may cause 4 bytes to be used on a 32-bit platform (or 8 bytes on a 64-bit platform). This is an old trick that comes from the observation that allocated memory takes up at least 4 or 8 bytes, and are aligned in such a way that the least significant bit or three will be zero.

Javascript engines (for example V8) are implemented using C++. You can find documentation about the size of boolean values in C++ spec. [1]

More information:
[1] ––

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The function sizeOf doesn't work with Uint8Array and other standard types of arrays.

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Thankyou, it works

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begoat commented Mar 26, 2020


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If someone looking for npm library to calculate size of an object in memory then give a try to this library:

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   `         bytes += obj.length * 2;`  why  obj.length*2 ,it should be Buffer.byteLength(str)

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why bytes += obj.toString().length * 2;

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0xhex commented May 19, 2021

i am getting error :
node:1863) UnhandledPromiseRejectionWarning: RangeError: Maximum call stack size exceeded
at Buffer.toString (buffer.js:776:46)

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kriit24 commented Nov 12, 2021

Im getting same error
Uncaught RangeError: Maximum call stack size exceeded

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