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simonom

parseJSON gotcha with reserved words

in Using jQuery • 9 years ago

Hi All

Just a note to let you know of an issue I encountered with parseJSON and an array of database results from php.

Didn't notice at the time but the database table the results were coming from had column names the same as reserved javascript words i.e. length and range.

So when the array was passed through to parseJSON the created object was completely screwed up.

Took a while to figure out what was happening.

Not sure if anything can be done but this should at least help someone else.

Simon

Replies(9)

jakecigar

Re: parseJSON gotcha with reserved words

9 years ago

parseJSON doesn’t care about JavaScript reserved names.

z='{"length":"3","range":"4"}'
x=$.parseJSON(z)

works fine. How was your JSON different?

JΛ̊KE

simonom

Re: parseJSON gotcha with reserved words

9 years ago

Well it did for me. Maybe it was because it was part of a geoJSON response, or the fact that length/range weren't in the top level.

Below is an example I quickly hacked up after working around it:

{ "type": "FeatureCollection", "features": [ {"type": "Feature", "geometry": {"type":"LineString","coordinates":[[1771873.3744905395,5914546.578293778],[1771893.7264727666,5914543.7359237932],[1772093.2272581572,5914518.1934995847]]}, "properties": {"id":"12345","range":"12 - 19","length":"123.67","road_1":"Some Street"},"id":"12345"} ]}

It validates fine through jsonlint. I was parsing through using two loops, loop through the features, t hen loop through the properties to get the attributes out:

var obj = jQuery.parseJSON(data);

$.each(obj.features, function (key, val) {

$.each(val.properties, function(col,value){

// Process the query row data.

If I left the attribute column names as length and range then things were definitely screwy.

Simon

jakecigar

Re: parseJSON gotcha with reserved words

9 years ago

parseJSON parses your code.

I don’t see how a couple of each calls could make things go screwy.

Can you make a demo page that shows the screwiness?

JΛ̊KE

simonom

Re: parseJSON gotcha with reserved words

9 years ago

Ok, try the following on jsfiddle:

http://jsfiddle.net/H9syp/

When you click on works, you get the alerts showing column and value.

When you click on doesn't work you get 0 undefined, 1 undefined, 2 undefined ..... and this keeps going for a very long time

jakecigar

Re: parseJSON gotcha with reserved words

9 years ago

LOL! $.parseJSON works fine.

BUT, $.each doesn’t!

z='{ "length":"33", "text":"foo"} '
x=$.parseJSON(z)
$.each(x,function(k,v){
console.log(k,v)
})

The code inside $.each blindly checks to see if length is in the object/array. If it’s there, it’s treated as an array, even when it’s not (the test cases). This is done for array-like objects that need to be treated as arrays.

Bottom line. $.parseJSON is innocent. $.each is guilty.

I think it is a bug, so I filed a bug report http://bugs.jquery.com/ticket/12130

JΛ̊KE

dave.meth..

Re: parseJSON gotcha with reserved words

9 years ago

$.each depends on the ability to treat array-like objects that way. It can't be changed.

jakecigar

Re: parseJSON gotcha with reserved words

9 years ago

Dave, should we suggest users not use $.each if they might ever have a property named length?

JΛ̊KE

simonom

Re: parseJSON gotcha with reserved words

9 years ago

Cheers for that.

Wasn't sure if anything could be done, but put it out there to warn someone else as it took me a few hours to figure out what the hell was going on with certain returns.

Thanks for the responses.

Simon

jakecigar

Re: Re: parseJSON gotcha with reserved words

9 years ago

Thanks for sharing! When I saw it happening before my eyes, I remembered about array-like objects!

This replacement for $.each will work with Objects with length properties that may look array-like, but aren’t.

jQuery.eachJSON = function(json,callback){
for (var element in json) {
if ( callback.call(json[element],element,json[element]) === false){
break;
}
}
}

JΛ̊KE

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