Javascript array.forEach范围？

Question

The console.log on line 9 shows

{ 'count' : 1111111 , 'average' : 2222222 , 'total' : 3333333 }

for all 3 array elements even though the loop that makes those changes has not run yet. How is this possible?

function test11(){

    var test = [
        { 'count' : 1 , 'average' : 2 , 'total' : 3 } ,
        { 'count' : 10 , 'average' : 20 , 'total' : 30 } , 
        { 'count' : 100 , 'average' : 200 , 'total' : 300 }
    ] ; 

    console.log( test ) ; 

    test.forEach( function( element , service_index , array ){

        array[ service_index ].count = 1111111 ;
        array[ service_index ].average = 2222222 ;
        array[ service_index ].total = 3333333 ;

    });

    console.log( test ) ;

    return ; 

}

Here is a jsfiddle of the code http://jsfiddle.net/d46wh2cv/7/ .

I read the specs at :

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

but I don't see any explanation for this counter intuitive behavior.

I am running Debian Linux with Google chrome 39.0.2171.95 and have also had the same result in Iceweasel 24.5.0.

Thanks for the help.

Answer 1

You're logging a reference to an object (since Arrays are an instance of the global Array object).

You're right that the loop hasn't run at the time of the log line, but that doesn't matter. By the time you inspect it, the values have already changed (since the loop probably takes all of 2 or 3 milliseconds to run).

Try logging just test[0].count instead of the whole object.