I was trying to change a file's name before uploading in my react.js application:

Here is the approach :

onInputChange = (e) =>{

    let newFileName='dp';
    if(e.target.files.length!==0){
        this.state.file=e.target.files[0];

        Object.defineProperty(this.state.file.name, 'name', {
            writable: true,
            value: newFileName
        });
        console.log(this.state.file);
    }
};

But the problem is, whenever this function gets called, I get an error saying : Object.defineProperty called on non-object

How this can be solved ?

I was trying to change a file's name before uploading in my react.js application:

Here is the approach :

onInputChange = (e) =>{

    let newFileName='dp';
    if(e.target.files.length!==0){
        this.state.file=e.target.files[0];

        Object.defineProperty(this.state.file.name, 'name', {
            writable: true,
            value: newFileName
        });
        console.log(this.state.file);
    }
};

But the problem is, whenever this function gets called, I get an error saying : Object.defineProperty called on non-object

How this can be solved ?

• javascript
• reactjs
• defineproperty

2 Answers 2

You are defining a new property on a string primitive in the Object.defineProperty. The this.state.file.name is a string primitive not an object.

const onInputChange = (e) =>{
    
        let newFileName='dp';
        if(e.target.files.length!==0){
            const file = e.target.files[0];
            // file is an object
            // Since file.name is read-only, this is not the proper way to change the name
            // For a file object writable is already true
            Object.defineProperty(file , 'name', {
                value: newFileName
            });
            console.log(file.name);
   
            // Since file name is readonly, and cannot be changed after the File is created
            // This is an alternate way to set the name on a copy of the file object
            const blob = file.slice(0, file.size, file.type); 
            newFile = new File([blob], newFileName, {type: file.type});
            console.log(newFile.name);
       }
};
document.querySelector("#fileInput").addEventListener("change", onInputChange);

Upload here:
<input type="file" name="test" id="fileInput"/>

Also to update the state do not directly mutate the this.state but instead use the setState() method to update it.

this.state.file.name is a string, not an object, right? Maybe you meant this.state.file? And it's not a new property. You're just changing the value. So why not this.state.file.name = newFileName?

And as Maifee points out, you may want file.filename, not file.name.