Having trouble retrieving a value from the img.onload event handler. A 'boolean' type error is being thrown, indicating it cannot be assigned to type '(this: GlobalEventHandlers, ev: Event) => any'

In my Angular application, I have implemented a method that verifies the size and dimensions of an image file and returns either false or true based on the validation result. Below is the code snippet for this function:

checkFileValidity(file: any, multiple: boolean): any {
    const reader = new FileReader();
    const img = new Image();
    img.src = window.URL.createObjectURL(file);
    reader.readAsDataURL(file);
    return img.onload = function () {
      const tableError = []
      const width = img.width;
      const height = img.height;
      console.log(img.width);
      console.log(img.height);
      if (file.size > 3000000) {
        console.log('size');
        tableError.push('size');
      }
      if (width < 1919 || height < 1079) {
        console.log('dimension');
        tableError.push('dimension');
      }
      if (tableError.length > 0 && !multiple) {
        return false;
      } else if (tableError.length > 0) {
        console.log('size+dimension');
        return false;
      }
      return true;
    }()
  }

I encountered an error at the line "return img.onload = function () {". How can I resolve this issue?

Answer №1

When you place the parentheses () immediately after the closing bracket } of your function assigned to img.onload, you are causing it to be invoked right away. As a result, the function executes and returns either true or false. Essentially, what is happening in this scenario is:

return img.onload = true;

This leads to an error being triggered. To resolve this issue, refrain from including the invoking parentheses () following the function body.

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