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Check if variable contains File or Blob

Javascript has both File

, and Blob

to represent files, and both of them are almost the same. Is there a way to check if a variable is datatyped File

or not Blob

?

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4 answers


W3.org:

'The File object is a Blob object with a name attribute, which is a string;'

In the case of a file:

var d = new Date(2013, 12, 5, 16, 23, 45, 600);
var generatedFile = new File(["Rough Draft ...."], "Draft1.txt", {type: 'text/plain', lastModified: d});

console.log(typeof generatedFile.name == 'string'); // true


In case of Blob:

var blob = new Blob();
console.log(typeof blob.name); // undefined

Condition:

var isFile = typeof FileOrBlob.name == 'string';
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The easiest way:



a = new File([1,2,3], "file.txt");
b = new Blob([1,2,3]);
c = "something else entirely";

a instanceof File
> true
b instanceof File
> false
c instanceof File
> false
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Compare the constructor class:

var b = new Blob()
console.log(b.constructor === Blob) // true
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This works for me when trying to determine if an object is a file:

var reader = new FileReader();

if(file.type){
    reader.readAsDataURL(file);
}

If I want to check if it is a specific file type, like an image, I do this:

if(file.type && file.type.indexOf('image') !== -1){
    reader.readAsDataURL(file);
}
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