File length in javascript

JavaScript file upload size validation

Yes, you can use the File API for this.

Here’s a complete example (see comments):

document.getElementById("btnLoad").addEventListener("click", function showFileSize() < // (Can't use `typeof FileReader === "function"` because apparently it // comes back as "object" on some browsers. So just see if it's there // at all.) if (!window.FileReader) < // This is VERY unlikely, browser support is near-universal console.log("The file API isn't supported on this browser yet."); return; >var input = document.getElementById('fileinput'); if (!input.files) < // This is VERY unlikely, browser support is near-universal console.error("This browser doesn't seem to support the `files` property of file inputs."); >else if (!input.files[0]) < addPara("Please select a file before clicking 'Load'"); >else < var file = input.files[0]; addPara("File " + file.name + " is " + file.size + " bytes in size"); >>); function addPara(text)

Slightly off-topic, but: Note that client-side validation is no substitute for server-side validation. Client-side validation is purely to make it possible to provide a nicer user experience. For instance, if you don’t allow uploading a file more than 5MB, you could use client-side validation to check that the file the user has chosen isn’t more than 5MB in size and give them a nice friendly message if it is (so they don’t spend all that time uploading only to get the result thrown away at the server), but you must also enforce that limit at the server, as all client-side limits (and other validations) can be circumvented.

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What is items and length in FileList in javascript

(very short) please go on and copy and past this in your code editor and then open in google. after you have opened this in your google browser then open its developer tool and write this in its console document.getElementById(‘up_file’).files then it returns FileList (please expand this object) Now when we have to upload a file and want to get the name of that file then we have to write the code document.getElementById(‘up_file’).files[0].name then it returns the file name says flower.jpg

Case 1

when you have expanded the object FileList you have noticed that there is an property name length . Now when you type document.getElementById(‘up_file’).files[length] then it should return 1 because when you had expanded FileList object you have seen their the property length is 1 but unexpectedly when we write document.getElementById(‘up_file’).files[length] it returns another object then 1 ! that object is: File and if we write document.getElementById(‘up_file’).files[length].name it returns the same thing which is returned by document.getElementById(‘up_file’).files[0].name that is the name of that file!

Question:

1) why do javascript returns an object insted of the length of the number of the files when we write document.getElementById(‘up_file’).files[length] ?

Case2

in that FileList object there is another property name item before you have expanded it but when you expand FileList object there is no property there with the name of item but when you further go on expanding the FileList object then you can see that item (may be this is a constrocter, may be, i am not sure, 50%). see, typeof __proto__ is a object then item can be accessed by by using dot(.) nation but it always returned undefined when i write __proto__.item . i am not going to further explain because i am going out of my point.

Question:

1) What is this Item? 2> how to get the properties of __proto__ object? well actually i so much confused and when i searched on internet then i get more puzzled! You may dislike this question because it is. you know a bit confusing Thanks for all your answers.

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getting file size in javascript

Do you have a webserver able to access C: ? If your OS is on C: , I advise against that, but first things first.

10 Answers 10

If it’s not a local application powered by JavaScript with full access permissions, you can’t get the size of any file just from the path name. Web pages running javascript do not have access to the local filesystem for security reasons.

HTML5 has the File API. If a user selects the file for an input[type=file] element, you can get details about the file from the files collection:

@Andrey: Other web applications use Java or Flash. I updated my answer with a link to the popular SWFUpload.

@Andrey Other script tools such as Flash, ActiveX, etc can access the local file system. Alternatively, certain server-side techniques can be used to monitor file upload progress and feed that information back when javascript requests it

@Andrey: that is not a cross-browser solution either. I don’t think Firefox exposes the fileSize property, it’s certainly not part of the standard. It might also only work for valid images and not other files.

You could probably try this to get file sizes in kB and MB Until the file size in bytes would be upto 7 digits, the outcome would be in kbs. 7 seems to be the magic number here. After which, if the bytes would have 7 to 10 digits, we would have to divide it by 10**3(n) where n is the appending action . This pattern would repeat for every 3 digits added.

let fileSize = myInp.files[0].size.toString(); if(fileSize.length < 7) return `$kb` return `$<(Math.round(+fileSize/1024)/1000).toFixed(2)>MB` 

If you could access the file system of a user with javascript, image the bad that could happen.

However, you can use File System Object but this will work only in IE:

function showFileSize() < let file = document.getElementById("file").files[0]; if(file) < alert(file.size + " in bytes"); >else < alert("select a file. duh"); >>

It’s 2022 and of course this is possible by using fetch to get the file and returning a blob , then reading the size property of the returned blob. However this works if you run a local server, as it’s not possible to access the local file system with Javascript (see the Note below).

function getFileStats(url) < let fileBlob; fetch(url).then((res) =>< fileBlob = res.blob(); return fileBlob; >).then((fileBlob)=>< // do something with the result here console.log([fileBlob.size, fileBlob.type]); >); > // Example of usage getFileStats('http://127.0.0.1:5500/img/mobileset/1.jpg'); // You should get something like this in the console [195142, 'image/jpeg'] 

Both the size and type properties have good browser coverage currently. Size is expressed in bytes, so roll your own formula to convert. This is just a quick example. It can be written better and adapted to your case. Processing a large number of files as blobs in the browser is likely to be a very compute-intensive task, especially for low-end computers, so use this accordingly.

Note: Javascript could never do this for a file on the local computer (at path C:\file.jpg) like in your example, because it’s not supposed to do this by design. It would be a major security risk to allow web pages direct access to the local file system, it’s only done through two filters: how the OS allows it through its API and how the browser allows it knowing that it needs to never expose the local file system to the internet. So my example will work if you run a server locally and can fetch the file through the server. Or if you fetch it from a remote server, if it allows.

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Blob: size property

The Blob interface’s size property returns the size of the Blob or File in bytes.

Value

The number of bytes of data contained within the Blob (or Blob -based object, such as a File ).

Examples

HTML

input type="file" id="input" multiple /> output id="output">Choose files…output> 

output  display: block; margin-top: 16px; > 

JavaScript

const input = document.getElementById("input"); const output = document.getElementById("output"); input.addEventListener("change", (event) =>  output.innerText = ""; for (const file of event.target.files)  output.innerText += `$file.name> has a size of $file.size> bytes.\n`; > >); 

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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This page was last modified on Apr 7, 2023 by MDN contributors.

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