Unable to make a reference to this in TypeScript

Question

Unable to make a reference to this in TypeScript

In my Angular2 application, I have a file upload feature that sends files as byte arrays to a web service. To create the byte array, I am using a FileReader with an onload event. However, I am encountering an issue where I cannot reference my uploadService within this event using this.uploadService.

public uploadHandler(event) {
    var reader = new FileReader();
    reader.onload = function() {
        var arrayBuffer = this.result, array = new Uint8Array(arrayBuffer), binaryString = String.fromCharCode.apply(null, array);
        //this.uploadService.DoUpload(binaryString);
    }
    reader.readAsArrayBuffer(event.files[0]);
}

I attempted to use the fat arrow function, but then I could no longer reference the result variable.

reader.onload = () => {
   //this.result does not exist anymore!
    var arrayBuffer = result, array = new Uint8Array(arrayBuffer), binaryString = String.fromCharCode.apply(null, array);
    this.uploadService.DoUpload(binaryString);
}

angular typescript

Answer 1

Answer №1

Using the fat arrow is considered best practice when it comes to handling events. Another way to access the data would be through the reader variable instead of directly referencing 'this'. Here's an example:

public handleUpload(event) {
    var reader = new FileReader();
    reader.onload = () => {
        var arrayBuffer = reader.result;
        var array = new Uint8Array(arrayBuffer);
        var binaryString = String.fromCharCode.apply(null, array);
        this.uploadService.PerformUpload(binaryString);
    };
    reader.readAsArrayBuffer(event.files[0]);
}

Answer 2

Using the fat arrow is considered best practice when it comes to handling events. Another way to access the data would be through the reader variable instead of directly referencing 'this'. Here's an example:

public handleUpload(event) {
    var reader = new FileReader();
    reader.onload = () => {
        var arrayBuffer = reader.result;
        var array = new Uint8Array(arrayBuffer);
        var binaryString = String.fromCharCode.apply(null, array);
        this.uploadService.PerformUpload(binaryString);
    };
    reader.readAsArrayBuffer(event.files[0]);
}

Answer 3

Answer №2

Why not give it a shot:

reader.onload = (event: any) => {
  console.log(event.target.result); // expecting result
};

Answer 4

Why not give it a shot:

reader.onload = (event: any) => {
  console.log(event.target.result); // expecting result
};

Answer 5

Answer №3

It seems like the issue you are experiencing might be related to the this binding problem. Here is a potential solution that could help resolve this issue:

function handleUpload(event) {
    var reader = new FileReader();
    var self = this;
    reader.onload = function() {
        var arrayBuffer = this.result;
        var array = new Uint8Array(arrayBuffer);
        var binaryString = String.fromCharCode.apply(null, array);
        
        // Call the upload service method
        self.uploadService.doUpload(binaryString);
    }
    
    reader.readAsArrayBuffer(event.files[0]);
}

Answer 6

It seems like the issue you are experiencing might be related to the this binding problem. Here is a potential solution that could help resolve this issue:

function handleUpload(event) {
    var reader = new FileReader();
    var self = this;
    reader.onload = function() {
        var arrayBuffer = this.result;
        var array = new Uint8Array(arrayBuffer);
        var binaryString = String.fromCharCode.apply(null, array);
        
        // Call the upload service method
        self.uploadService.doUpload(binaryString);
    }
    
    reader.readAsArrayBuffer(event.files[0]);
}

Unable to make a reference to this in TypeScript

Answer №1

Answer №2

Answer №3

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