Why is there a function in my javascript array?

Question

The following code loops over an array. It is running within a casperJS script and therefore a phantomJS headless browser environment

socket.on('list', function(data){
                console.log("Message", JSON.stringify(data)); //no func def in this data
                var localMatchStore= [];
                for (var i in data.matches) {
                   localMatchStore.push(data.matches[i]);
                }
                console.log(localMatchStore);

            });

This returns the data I expect but also a function definition as the last item in the array. Why is this?

0580:MS101:2014,0580:MS127:2014,0580:MS128:2014,0901:LS162:2014,function () {
        for(var i=0,sum=0;i<this.length;sum+=this[i++]);
        return sum;
    }

Lloyd · Accepted Answer · 2014-01-14 10:23:49Z

1

Try using hasOwnProperty() with your for..in. That loop construct can include members of the object that are inherited through the prototype chain. hasOwnProperty() ensures that the property is a direct member.

socket.on('list', function(data){
    console.log("Message", JSON.stringify(data)); //no func def in this data

    var localMatchStore= [];

    for (var i in data.matches) {
        if (data.matches.hasOwnProperty(i)) localMatchStore.push(data.matches[i]);
    }

    console.log(localMatchStore);

});

For a more in-depth discussion of this function see here on MDN.

answered Jan 14, 2014 at 10:23

Lloyd

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