Significant issue identified with ajax functionality, requiring immediate attention

Question

Significant issue identified with ajax functionality, requiring immediate attention

After executing the code in the console, I expected to see the ajax object with a readyState of 0 (as I aborted the ajax call). However, Chrome is displaying the number 4 in the console instead of 0. This discrepancy is surprising.

http://jsfiddle.net/8yCfn/1/

temp = new XMLHttpRequest();

temp.open("POST","http://jsfiddle.net/",true);

temp.onreadystatechange = function() {

    console.log(temp);
    console.log(temp.readyState);

};

temp.send(null);

temp.abort();

Can someone help resolve this issue with Chrome? I plan to report it as a bug but would appreciate insights from those more knowledgeable than myself.

--

ATTENTION:

It seems my question went unanswered.

temp = new XMLHttpRequest();

temp.open("POST","http://jsfiddle.net/",true);

temp.onreadystatechange = function() {

console.log(temp);
console.log(temp.readyState);

};

temp.send(null);

temp.abort(); Why does the readyState property of the temp object show differently when printed in the console? It should be consistent, regardless of browser behavior.

If an object's property xxx is set to 0, then object.xxx MUST be 0, as illustrated by this example showing the bug.

javascript ajax

Answer 1

Answer №1

If you wish to view the readyState zero [unset], it must be done outside of the onreadystatechange handler and prior to triggering open.

temp = new XMLHttpRequest();
temp.onreadystatechange = function() {
    console.log(temp.readyState);
};
console.log(temp.readyState);
temp.open("POST",window.location.href,true);
temp.send(null);

The console output will be as follows:

0 
1 
2 
3 
XHR finished loading: "http://fiddle.jshell.net/_display/".
4

Now, let's consider aborting

temp = new XMLHttpRequest();
temp.onreadystatechange = function() {
    console.log("orsc:", temp.readyState);
};
console.log("Before Open: ", temp.readyState);
temp.open("POST",window.location.href,true);
temp.send(null);
temp.abort();
console.log("After abort: ", temp.readyState);

Console output will show:

Before Open: 0 
orsc: 1 
orsc: 4 
After abort: 0

This behavior aligns with what is specified in the final steps of the Spec

6. If the state is UNSENT, OPENED with the send() flag being unset, or DONE, proceed to the next step.
   Otherwise, follow these substeps:
        Change the state to DONE.   <---- Set to 4
        Unset the send() flag.
        Fire an event named readystatechange.    <---- Event fired onreadystate change
        ...
7. Reset the state to UNSENT.      <---- Set to 0
    No readystatechange event is triggered.

In simpler terms, it instructs to set the ready state to 4 and trigger onreadystatechange. Then, it directs to reset the ready state to zero without invoking a new onreadystatechange. This explains why the example displays a 4 followed by a 0.

Before Open: 0 
orsc: 1 
orsc: 4          <--Abort step 6 - set to done, fire readystatechange
After abort: 0   <--Abort step 7 - set to zero, don't fire readystatechange

An Explanation Regarding Console Behavior

You mentioned:

It does not clarify why console.log(a) displays "readyState"=>0 while console.log(a["readyState"]) shows 4.

This discrepancy occurs because console.log(a) refers to the object itself! The console doesn't show the value at recording time but when viewed, adjusting dynamically!

A simple browser demo illustrates this point clearly.

JSFiddle: http://jsfiddle.net/4RDh3/

Answer 2

If you wish to view the readyState zero [unset], it must be done outside of the onreadystatechange handler and prior to triggering open.

temp = new XMLHttpRequest();
temp.onreadystatechange = function() {
    console.log(temp.readyState);
};
console.log(temp.readyState);
temp.open("POST",window.location.href,true);
temp.send(null);

The console output will be as follows:

0 
1 
2 
3 
XHR finished loading: "http://fiddle.jshell.net/_display/".
4

Now, let's consider aborting

temp = new XMLHttpRequest();
temp.onreadystatechange = function() {
    console.log("orsc:", temp.readyState);
};
console.log("Before Open: ", temp.readyState);
temp.open("POST",window.location.href,true);
temp.send(null);
temp.abort();
console.log("After abort: ", temp.readyState);

Console output will show:

Before Open: 0 
orsc: 1 
orsc: 4 
After abort: 0

This behavior aligns with what is specified in the final steps of the Spec

6. If the state is UNSENT, OPENED with the send() flag being unset, or DONE, proceed to the next step.
   Otherwise, follow these substeps:
        Change the state to DONE.   <---- Set to 4
        Unset the send() flag.
        Fire an event named readystatechange.    <---- Event fired onreadystate change
        ...
7. Reset the state to UNSENT.      <---- Set to 0
    No readystatechange event is triggered.

In simpler terms, it instructs to set the ready state to 4 and trigger onreadystatechange. Then, it directs to reset the ready state to zero without invoking a new onreadystatechange. This explains why the example displays a 4 followed by a 0.

Before Open: 0 
orsc: 1 
orsc: 4          <--Abort step 6 - set to done, fire readystatechange
After abort: 0   <--Abort step 7 - set to zero, don't fire readystatechange

An Explanation Regarding Console Behavior

You mentioned:

It does not clarify why console.log(a) displays "readyState"=>0 while console.log(a["readyState"]) shows 4.

This discrepancy occurs because console.log(a) refers to the object itself! The console doesn't show the value at recording time but when viewed, adjusting dynamically!

A simple browser demo illustrates this point clearly.

JSFiddle: http://jsfiddle.net/4RDh3/

Answer 3

Answer №2

In various other browsers as well, the XMLHttpRequest can exhibit similar behavior. According to the specification, when the request is aborted, the readyState property transitions to 4 before reverting back to 0.

This means that even if a request is aborted, checking for the onchange event may still return a readyState value of 4.

You can determine if the user specifically aborted the request by using the following expression:

!xhr.getAllResponseHeaders();

Where xhr represents the XMLHttpRequest object, and this expression will evaluate to true if the request was indeed terminated by the user.

The reality is that browsers may not strictly adhere to the specifications. While it states that the readyState should be set to 0 when the user aborts, each browser implementation may introduce its own quirks before eventually complying with the specified behavior.

Answer 4

In various other browsers as well, the XMLHttpRequest can exhibit similar behavior. According to the specification, when the request is aborted, the readyState property transitions to 4 before reverting back to 0.

This means that even if a request is aborted, checking for the onchange event may still return a readyState value of 4.

You can determine if the user specifically aborted the request by using the following expression:

!xhr.getAllResponseHeaders();

Where xhr represents the XMLHttpRequest object, and this expression will evaluate to true if the request was indeed terminated by the user.

The reality is that browsers may not strictly adhere to the specifications. While it states that the readyState should be set to 0 when the user aborts, each browser implementation may introduce its own quirks before eventually complying with the specified behavior.

Answer 5

Answer №3

Seems like my question went unnoticed.

temp = new XMLHttpRequest();

temp.open("POST","http://jsfiddle.net/",true);

temp.onreadystatechange = function() {

    console.log(temp);
    console.log(temp.readyState);

};

temp.send(null);

temp.abort();

Why is it that in the first line of the console, the object temp shows readyState property as 0, but then in the second line it displays 4? It's confusing that they are different despite consistent browser behavior.

If an object has a property xxx set to 0, then object.xxx MUST be 0 - not 4 as demonstrated by this bug in my example.

Answer 6

Seems like my question went unnoticed.

temp = new XMLHttpRequest();

temp.open("POST","http://jsfiddle.net/",true);

temp.onreadystatechange = function() {

    console.log(temp);
    console.log(temp.readyState);

};

temp.send(null);

temp.abort();

Why is it that in the first line of the console, the object temp shows readyState property as 0, but then in the second line it displays 4? It's confusing that they are different despite consistent browser behavior.

If an object has a property xxx set to 0, then object.xxx MUST be 0 - not 4 as demonstrated by this bug in my example.

Significant issue identified with ajax functionality, requiring immediate attention

Answer №1

Answer №2

Answer №3

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