Loading a PDF in an <object> tag, I want to show an indicator while the document is being loaded instead of just an empty element, so I positioned a Load Panel over the <ob,javascript,google-chrome,dom-events"/>

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Loading a PDF in an <object> tag, I want to show an indicator while the document is being loaded instead of just an empty element, so I positioned a Load Panel over the <ob

javascript - onload not firing in Chrome

Loading a PDF in an <object> tag, I want to show an indicator while the document is being loaded instead of just an empty element, so I positioned a Load Panel over the <ob

问题描述

Loading a PDF in an <object> tag, I want to show an indicator while the document is being loaded instead of just an empty element, so I positioned a Load Panel over the <object>. I added a function to hide the panel:

function documentLoaded() {
    // Code to hide panel here.
}

And set it to fire in the onload event of the <object> tag:

<object type="application/pdf" data="/documents/sample.pdf" onload="documentLoaded();"></object>

This is working exactly how I want it to in Firefox and in Edge, but when I tested it in Chrome the Load Panel never went away. When I debugged it I saw that the documentLoaded() function was never called at any point.

Is there another way to get this to work with Chrome, or another way completely to call a JS function once the PDF is ready?

The problem is that you're not overriding the Compare() method of the base class Vector in VectorND and Vector3D. Instead, you're declaring new methods that take an object of the same type (VectorND or Vector3D) in your subclasses. The original Compare() method of the base class is still available in the subclasses, and it's that method that get's called when you call A.Compare(B).

To make it more clear, you have 

Vector{
    public boolean Compare(Vector vec){ ... }
}

class Vector3D extends Vector {
    public boolean Compare(Vector vec){ ... }
    public boolean Compare(Vector3D vec){ ... } 
}

class VectorND extends Vector {
    public boolean Compare(Vector vec){ ... }
    public boolean Compare(VectorND vec){ ... } 
}

So when you call 

A.Compare(B)

and there is no Compare(Vector3D) declared in class VectorND, what you're really doing is calling

Vector.Compare(Vector)

since both A and B are derived from the base class Vector.

If you really want to override the Compare method in Vector with the ones in your subclasses, you need to declare them identically in the subclasses (i.e. with the same type of parameter).

And if you really want the method to throw an exception in the specified case, you need to explicitly check the type of the Vector by using the instanceof operator, and throw an exception if it's not the same type.

public class Vector3D extends Vector {
    @Override
    public boolean Compare(Vector vec){
        if( !(vec instanceof Vector3D) )
            throw new IllegalArgumentException("Vector3D can only be compared to Vector3D!");

        // Compare and return true or false
    }
}

The @Override annotation indicates that you intended to override a method in the base class. If there is no matching method in the base class, for example if you try to do

@Override
public boolean Compare(Vector3D vec)

the compiler/IDE will issue an error to notify you that you're not overriding anything (since the Vector class has no Compare(Vector3D vec) method).

标签： javascriptgoogle-chromedom-events

解决方案

document.querySelector('#load_panel').onload=documentLoaded()

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